Add persistent sketch-constraint system (ocs_gcs port) and named-parameters handoff docs

Ports FreeCAD's planegcs 2D geometric constraint solver to Rust as a new
crates/ocs_gcs workspace member, and wires it into the document/scene model
as a persistent SketchConstraintSet: Coincident, Horizontal/Vertical,
Parallel/Perpendicular, Equal, Tangent, Distance, Angle and Radius
constraints that re-solve live (including mid-drag, not just on release),
render glyphs and a DOF badge, flag conflicts with a one-click resolver
pill, and round-trip through save/load via an XRecord blob.

Also includes docs/command_reference.md (a statically generated reference
of every registered command and its prompt sequence) and
docs/named_parameters_design.md + docs/backlog.md, which hand off the next
queued feature (a named-parameter/expression table) and consolidate every
deliberate scope-down and open gap found along the way, so a fresh session
has a complete starting point.

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

src/app/update/mod.rs

@@ -3292,6 +3292,10 @@ impl OpenCADStudio {
                 }
                 Task::none()
             }
+            Message::ResolveOneSketchConflict => {
+                self.resolve_one_sketch_conflict();
+                Task::none()
+            }
             Message::TogglePolar => {
                 self.polar_mode ^= true;
                 if self.polar_mode {
@@ -5872,6 +5876,18 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::RibbonLabelFontSizeChanged(value) => {
+                self.ribbon.set_label_font_size(value);
+                self.save_config();
+                Task::none()
+            }
+
+            Message::RibbonGroupTitleFontSizeChanged(value) => {
+                self.ribbon.set_group_title_font_size(value);
+                self.save_config();
+                Task::none()
+            }
+
             Message::CrosshairColorChanged(value) => {
                 self.crosshair_color_input = value.clone();
                 if value.trim().is_empty() {