Add named parameters, UI scale setting, OPTIONS/OP dispatch, and help manual

Named parameters (docs/named_parameters_design.md, stages 3-4):
- ParameterTable (src/scene/named_parameters.rs): a document-wide table of
  named formulas, each resolved through a shared expression evaluator with
  cross-parameter references, cycle detection, and division-by-zero/parse
  error reporting. SketchConstraint::driving_param becomes DrivingValue
  (Literal | Named) instead of a bare f64, resolved at solve time by
  sketch_solve::build_constraint via Scene::named_parameters.
- Persistence (src/scene/named_parameters_persist.rs): same lazy XRecord
  model sketch_persist.rs already established, synced around open/save.
  Bumps the sketch-constraint XRecord's own format version (1 -> 2) since
  DrivingValue's shape doesn't line up with a version-1 blob's bytes.
- PARAMETERS command and its editor (src/ui/window/named_parameters.rs):
  add/remove/edit rows, live validation, duplicate-name detection: Apply
  defines the table and re-solves every constraint scope with a
  named-parameter-driven constraint (command_driver.rs). Distance/Angle
  constraint prompts (modules/draw/constrain/value.rs) now accept either a
  literal or an existing parameter's name, mirroring how the constraint's
  own value prompt already worked.
- Undo scope-down carried over from this project's own established pattern
  (constraint-system stage 9): the geometry an Apply moves is one undo
  step, but the parameter table edit itself has no undo entry yet — a
  documented follow-up, not a silent gap.

UI scale setting (src/app/settings.rs, app/mod.rs, ui/window/options.rs):
  a whole-interface scale percentage (50-200%), wired directly into iced's
  own per-window scale_factor hook rather than per-panel font-size
  plumbing, so it applies immediately to every panel, dialog, and the
  ribbon at once. Persisted alongside the existing lineweight-display-scale
  setting.

OPTIONS/OP command dispatch (app/commands/view.rs, app/commands/mod.rs):
  OPTIONS was registered for autocomplete but had no dispatch arm — the
  Start-tab welcome screen's own button was the only way to reach it.
  Found live-testing the UI-scale setting, unrelated to that feature
  itself. "OP" is AutoCAD's own short alias.

help/: a new self-contained static user-help manual (manual.md as the
authored source, tools/build_help.py splits it into the committed static
HTML pages plus search index) — not yet wired into the application.

64 new/updated tests across the named-parameters and constraint-prompt
changes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

help/manual.md

@@ -0,0 +1,305 @@
+# OpenCAD Studio User Manual
+
+This manual describes the user-facing workflows of OpenCAD Studio. The initial
+version establishes the help structure and high-level guidance; individual
+commands should be expanded and verified against released behavior before the
+manual is published as complete.
+
+## Getting Started
+
+### What OpenCAD Studio does
+
+OpenCAD Studio is a desktop and web CAD application for opening, creating,
+editing, visualizing, and saving two- and three-dimensional drawings. It works
+with DWG and DXF drawings and provides command-line, ribbon, automation, and
+plugin-oriented workflows.
+
+### A first drawing
+
+1. Create a new drawing or open an existing DWG or DXF file.
+2. Confirm the active workspace, units, layer, and object-snap settings.
+3. Create geometry with a drawing command such as **Line**, **Circle**, or
+   **Polyline**.
+4. Edit the result with grips or a modification command.
+5. Save the drawing under a new name until its compatibility has been verified.
+
+> **Data safety:** Keep an untouched copy of important third-party drawings.
+> Confirm geometry, layouts, external references, and plotted output before
+> replacing the original file.
+
+### How to use this manual
+
+Use the chapter navigation for broad workflows, the search box for a command or
+concept, and the previous/next links for sequential reading. Command names,
+system variables, keys, and file extensions appear in `monospaced text`.
+
+## Files and Drawings
+
+### Create and open drawings
+
+Use **New** for a blank document and **Open** for an existing DWG, DXF, backup,
+or autosave drawing. After opening a file from another CAD system, inspect its
+units, layers, blocks, fonts, raster references, layouts, and model extents.
+
+### Save and Save As
+
+**Save** updates the current drawing. **Save As** changes its path, format, or
+version. Prefer Save As when validating interoperability or recovering an older
+drawing. A successful write does not replace visual inspection of a reopened
+copy.
+
+### Recovery and backups
+
+OpenCAD Studio recognizes drawing backups and autosave-style files where the
+underlying data is DWG or DXF. If strict loading rejects malformed entities, use
+the recovery workflow and review what was discarded before continuing work.
+
+### External resources
+
+Raster images, underlays, fonts, materials, and external references may depend
+on paths outside the drawing. Keep referenced files together when moving a
+project and verify that relative paths still resolve.
+
+## Workspace and Navigation
+
+### Model space and paper space
+
+Model space is the primary drawing environment. Paper-space layouts arrange
+views for plotting through layout viewports. Always confirm the active space
+before drawing or editing.
+
+### Pan, zoom, and orbit
+
+Use pan and zoom to navigate without changing drawing geometry. Use orbit and
+view controls for three-dimensional inspection. **Zoom Extents** is useful when
+the drawing appears empty or geometry is far from the expected location.
+
+### Multiple model viewports
+
+Model viewports can show different views of the same document. Grid, snap,
+camera, and render mode may vary by viewport; confirm which viewport is active
+before entering coordinates.
+
+### Selection and object snaps
+
+Selection identifies the objects a command will modify. Object snaps target
+precise geometric locations such as endpoints, midpoints, centers, and
+intersections. Zoom in and verify the snap marker when precision matters.
+
+## Create and Edit Geometry
+
+### Basic drawing commands
+
+Create lines, arcs, circles, ellipses, polylines, splines, points, text, hatches,
+and other supported entities from the ribbon or command line. Follow the active
+prompt: multi-step commands remain active until they complete or are cancelled.
+
+### Modify geometry
+
+Common modification workflows include move, copy, rotate, scale, mirror,
+offset, trim, extend, fillet, chamfer, stretch, join, explode, and erase. Locked
+layers can prevent modification.
+
+### Grips and direct manipulation
+
+Select an entity to expose its grips. Dragging a grip previews and then commits
+a geometric change. Constrained neighboring geometry may update with it.
+
+### Undo, redo, and OOPS
+
+**Undo** reverses recorded document operations and **Redo** reapplies them.
+**OOPS** restores the most recently erased entities without reversing later
+commands. Save before a risky sequence and verify that associated dimensions,
+hatches, groups, and constraints were restored with their geometry.
+
+## Layers and Properties
+
+### Layers
+
+Layers organize geometry and control visibility, locking, color, line type,
+line weight, and plot behavior. Set the intended active layer before creating
+objects. Avoid editing objects on locked layers.
+
+### Object properties
+
+Properties can be assigned explicitly or inherited **ByLayer** or **ByBlock**.
+Use the Properties surface or commands such as `CHPROP` to inspect and change
+selected objects.
+
+### Styles
+
+Text, dimension, multiline, table, and visual styles centralize presentation.
+Changing a shared style can update many objects, so inspect affected layouts
+before saving.
+
+## Blocks and References
+
+### Create and insert blocks
+
+A block definition groups reusable drawing content; an INSERT places an
+instance with its own position, rotation, scale, attributes, and optional array
+settings. Editing a definition affects every reference to it.
+
+### Array inserts
+
+Array inserts place multiple block instances with row and column counts and
+spacing. Large counts can generate substantial geometry. Validate scaled and
+rotated arrays when exchanging drawings with another CAD system.
+
+### Attributes and external references
+
+Attributes attach editable values to block references. External references and
+underlays retain links to other files; preserve their paths when sharing or
+archiving a project.
+
+## Annotation and Dimensions
+
+### Text and annotation
+
+Single-line text, multiline text, leaders, multileaders, tables, tolerances,
+center marks, and centerlines communicate design intent. Missing fonts can
+change layout or substitute glyphs, especially in the web build.
+
+### Dimensions
+
+Dimensions combine measured geometry with a dimension style. Associative
+dimensions update when their source geometry changes; non-associative or
+partially associated dimensions require manual verification.
+
+### Annotation scale
+
+Annotative objects can display differently at different viewport scales.
+Confirm the active annotation scale before creating annotations and inspect all
+paper-space viewports before plotting.
+
+## Layouts and Plotting
+
+### Layouts and viewports
+
+Layouts represent sheets. Paper-space viewports expose model-space views at
+controlled scales. Lock finished viewports to avoid accidental view changes.
+
+### Page setup and plot preview
+
+Choose the target device or file format, paper size, orientation, plot area,
+scale, style behavior, and output quality. Use preview to catch clipping,
+incorrect line weights, hidden layers, or an unintended plot area.
+
+### Export checks
+
+Before distributing a PDF or plotted file, compare it with the drawing at the
+intended sheet size and verify text, dimensions, raster content, transparency,
+line types, and viewport scales.
+
+## 3D Modeling and Visualization
+
+### Solids and surfaces
+
+OpenCAD Studio can create and display solid primitives and modeled features such
+as extrusions and revolutions. Imported ACIS-backed bodies are tessellated for
+display while exact body data is retained where supported.
+
+### Visual styles and lighting
+
+Wireframe, shaded, hidden-line, materials, lights, and shadows affect display,
+not the underlying object geometry. Switch to wireframe when diagnosing missing
+faces or material problems.
+
+### Tessellation quality
+
+Curves and analytic surfaces are converted into display geometry according to
+view and tolerance settings. A coarse display does not necessarily mean the
+stored curve or solid is coarse.
+
+## Parametric Constraints
+
+### Geometric constraints
+
+Constraints capture relationships such as coincident, horizontal, vertical,
+parallel, perpendicular, equal, tangent, distance, angle, and radius. Use the
+degree-of-freedom and conflict indicators to understand the sketch state.
+
+### Editing constrained geometry
+
+Moving or grip-editing constrained geometry can move neighboring objects. If a
+solve fails or becomes redundant, inspect the constraint glyphs and conflict
+status before deleting geometry.
+
+### Persistence and history limitations
+
+Constraint data is stored as OpenCAD Studio extension data inside DWG and DXF.
+Other applications may preserve it without interpreting it. Constraint edits
+and geometry changes may currently occupy adjacent history entries; verify the
+result after undo, redo, erase, copy, and reopen operations.
+
+## Commands and Shortcuts
+
+### Command line
+
+Enter a command name or alias, then respond to its prompts. Press `Escape` to
+cancel the active command and `Return` to accept an available default. Exact
+prompt options vary by command and current selection.
+
+### Discover commands
+
+Use command autocomplete and the ribbon to discover available operations. Some
+commands are one-shot actions; others maintain state across several point,
+number, keyword, or object-selection inputs.
+
+### Shortcut conventions
+
+Application and operating-system shortcuts can differ between native and web
+builds. Avoid assigning browser-reserved shortcuts to web-only workflows.
+
+## Automation and Plugins
+
+### Automation interface
+
+The automation interface can inspect documents, run commands, query geometry,
+capture the viewport, and perform batches. Callers should use request IDs and
+document revisions to avoid repeating or applying work to stale state.
+
+### Plugins
+
+Native plugins can contribute commands and ribbon surfaces through the plugin
+host. Install only trusted packages that match the host API, compiler, and CAD
+model compatibility requirements.
+
+### Native and web differences
+
+The browser build uses in-memory file workflows and cannot load native plugin
+libraries. Some rendering, font, windowing, and parallel-processing behavior
+also differs from the desktop build.
+
+## Troubleshooting and Recovery
+
+### A drawing opens incorrectly
+
+Check units, extents, layers, layouts, block placement, missing references, and
+fonts. Reopen a copy after saving to detect serialization problems early. Keep
+the original file available for comparison.
+
+### Geometry is missing or distorted
+
+Try Zoom Extents, enable relevant layers, switch to wireframe, and inspect block
+scale, array settings, clipping boundaries, object normals, and coordinates far
+from the origin.
+
+### Rendering is incomplete
+
+Reduce unusually large images or material textures, simplify extreme hatch or
+array inputs, and compare another visual style. Record the graphics backend and
+the smallest drawing that reproduces the issue.
+
+### Undo did not restore the expected state
+
+Stop editing and save a diagnostic copy. Try the next adjacent undo entry only
+when you understand what it represents. Compare the result with autosave or
+backup data before overwriting the original drawing.
+
+### Report a reproducible problem
+
+Include the OpenCAD Studio version, platform, native or web build, exact steps,
+expected and observed results, and a minimal sanitized drawing when possible.
+Do not publish confidential drawings or external-reference paths.
+