Render: integrated workspace, preview image jobs and opaque PBR (#1046)

Lands the Render workspace (R3), bounded preview-image jobs with cancellation and atomic PNG export (R4a), and opaque PBR looks as one change.

- Render workspace: an overlay-free product preview on the installed GPU device. Returning to Design restores its camera. render.scene and render.settings.apply are added.
- Image jobs: render.preflight/start/status/cancel/export run bounded CPU preview jobs. Export captures the job, overwrite choice and document, and checks the caller's file scope before writing.
- Opaque PBR: looks can carry metal fraction, roughness and dielectric IOR. The product viewport and preview PNG use them; geometry and mass are unchanged. The v1 catalog export refuses PBR rather than dropping it.
- Render setups and PBR looks are saved under design format 21. Labels are in en/de/ja/ko/zh/ru.

Supersedes #706 and #800. Refs #620, #673, #756, #1004.

Contributed by @0xlillith.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

docs/control-protocol.md

@@ -71,6 +71,10 @@ MCP server sends its folders this way on every request ([mcp.md](mcp.md)). Witho
 
 Commands never open dialogs when run this way. `solidcraft-cli commands` prints the same registry.
 
+Product images use `render.preflight/start/status/cancel/export` through `engine.execute`.
+Keep the returned session-scoped job ID for subsequent calls; status does not block or
+render. See [render jobs](render-jobs.md) for capture, cancellation and export semantics.
+
 While an interactive native file picker is open, `ui.inspect` reports `file_picker_busy: true`.
 Engine commands, `ui.file` and `ui.home` requests wait for its answer; window resizing,
 inspection and screenshots remain available.
@@ -97,7 +101,7 @@ unit regardless of the design, pass an expression with one: `"value": "50 mm"` o
 
 | Method | Params | Notes |
 |---|---|---|
-| `ui.inspect` | — | UI state, what is hidden (`visibility`: bodies, origin and construction items, sketches, joints (`hidden_joints`, joint ids); set it with the `browser.visibility` command), viewport rect, camera, active tool/dialog, the status line (`status`: text and whether it is an error), hover, renderer, timings, live preview (`active`, `busy`, `error`, `ms`, bodies it stands in for) |
+| `ui.inspect` | — | UI state, pending file picker (`file_picker_busy`; compatibility alias `file_dialog_open`, no path), what is hidden (`visibility`: bodies, origin and construction items, sketches, joints (`hidden_joints`, joint ids); set it with the `browser.visibility` command), viewport rect, camera, active tool/dialog, the status line (`status`: text and whether it is an error), hover, renderer, timings, live preview (`active`, `busy`, `error`, `ms`, bodies it stands in for) |
 | `ui.set` | any `UiState` field (`tab`, `perspective`, `showGrid`, `dark`, …), and `hiddenBodies`, `hiddenOrigin`, `hiddenSketches`, `shownSketches`, `hiddenJoints` (whole lists; `browser.visibility` changes single items) | `dark: false` switches to the light theme |
 | `ui.view` | `view`: `front`, `back`, `top`, `bottom`, `left`, `right`, `iso`, `home`, `fit`; `animate` (bool, default false: snap) | |
 | `ui.start` | `command` | like a toolbar click: starts the sketch tool or dialog for the command |
@@ -134,6 +138,10 @@ unit regardless of the design, pass an expression with one: `"value": "50 mm"` o
 | `ui.resize` | `width`, `height` | |
 | `app.quit` | `force?` (quit without asking about unsaved designs) | `quitting` (the window closes), `asking` (a "save changes?" prompt is open) |
 
+`ui.workspace {workspace?: "design" | "render"}` reads or changes the active workspace.
+Entering Render requires finishing the current modelling operation; returning restores
+the Design camera. See [the integrated Render workspace](render-workspace.md).
+
 ## MCP
 
 `solidcraft-cli mcp --connect 127.0.0.1:PORT` bridges an MCP client (an AI agent) to this