Add Properties-panel Constraints/Parameters sections, a constraint-pill

value toggle, and redesigned constraint-ribbon icons

Properties panel:
- New "Parameters" section (shown with no selection) listing every named
  parameter with inline name/formula editing, add, and delete, backed by
  new PropValue::ParamRow/ParamAddRow and command_driver handlers
  (resolve_named_parameter_edit, on_prop_param_commit/_delete/_add_new).
  A fresh parameter's formula now defaults to "1", not "0" — a 0-length
  seed value is a genuine solver singularity for a Distance constraint
  driven by that parameter, with no defined direction to grow back out of.
- New "Constraints" section (shown for a single selected entity) listing
  every constraint touching it as a clickable PropValue::EntityLink that
  selects the linked entities in the viewport, danger-tinted when the
  constraint conflicts.

Constraint pills:
- New Options > General toggle, "Show values and parameter names on
  constraint markers" (on by default, persisted). Off, every pill shows
  just its bare glyph instead of glyph+driven-value/parameter-name — the
  glyph alone is enough to see a constraint is present, without the value
  text covering nearby geometry on a dense sketch.

Constraint-ribbon icons:
- Replaced all 18 unicode/letter glyph icons (including the plain "F",
  "L", "M", "S" letters) with proper SVGs under assets/icons/constrain/,
  matching the Modify section's two-color style (#B4B6B9 white / #6DB7ED
  blue, consistent stroke width). Tangent reuses the Draw section's
  white-arc-plus-blue-dots motif.

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

src/app/update/file.rs

@@ -397,6 +397,7 @@ impl OpenCADStudio {
             backup_on_save: self.backup_on_save,
             file_assoc_enabled: self.file_assoc_enabled,
             write_dwg_native_constraints: self.write_dwg_native_constraints,
+            show_constraint_values: self.show_constraint_values,
             savetime_min: self.savetime_min,
             default_save_format: self.default_save_format.clone(),
             pick_add: self.pick_add,
@@ -467,6 +468,7 @@ impl OpenCADStudio {
         self.backup_on_save = s.backup_on_save;
         self.file_assoc_enabled = s.file_assoc_enabled;
         self.write_dwg_native_constraints = s.write_dwg_native_constraints;
+        self.show_constraint_values = s.show_constraint_values;
         self.savetime_min = s.savetime_min;
         self.default_save_format =
             crate::io::canonical_save_format(&s.default_save_format).to_string();

src/app/update/mod.rs

@@ -5949,6 +5949,28 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            // ── Parameters / Constraints sections embedded in the
+            // Properties panel ──────────────────────────────────────────────
+            Message::PropParamInput { index, field, value } => {
+                self.tabs[self.active_tab]
+                    .properties
+                    .edit_buf
+                    .insert(crate::ui::properties::FieldKey::Param(index, field), value);
+                Task::none()
+            }
+            Message::PropParamCommit { index, field } => self.on_prop_param_commit(index, field),
+            Message::PropParamDelete(index) => self.on_prop_param_delete(index),
+            Message::PropParamAddNew => self.on_prop_param_add_new(),
+            Message::PropConstraintLinkClick(handles) => {
+                let i = self.active_tab;
+                self.tabs[i].scene.deselect_all();
+                for h in handles {
+                    self.tabs[i].scene.select_entity(h, false);
+                }
+                self.refresh_properties();
+                Task::none()
+            }
+
             // ── Options / About windows ───────────────────────────────────
             Message::OptionsOpen => {
                 self.active_modal = Some(super::ModalKind::Options);
@@ -6312,6 +6334,11 @@ impl OpenCADStudio {
                 self.persist_settings_if_changed();
                 Task::none()
             }
+            Message::ShowConstraintValuesChanged(enabled) => {
+                self.show_constraint_values = enabled;
+                self.persist_settings_if_changed();
+                Task::none()
+            }
             Message::LanguageChanged(language) => {
                 if self.language == language {
                     return Task::none();