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/entities/curve.rs

@@ -422,9 +422,19 @@ pub fn entity_with_lwpolyline_world_xy(entity: &EntityType) -> EntityType {
     }
 }
 
+/// Fixed world-space tessellation angle used for on-screen wire points.
+///
+/// Finer than the kernel's own `DEFAULT_ANGLE` (7.5°, 48 segments per turn):
+/// 3° gives 120 segments per full turn, so a typical circle at typical zoom
+/// no longer shows its polygon joints. Still a fixed world-space angle rather
+/// than one adaptive to view scale, so an aggressively zoomed-in view can
+/// still reveal facets — it raises the zoom threshold rather than removing
+/// the ceiling.
+const DISPLAY_ANGLE: f64 = std::f64::consts::PI / 60.0;
+
 /// World-space wire points sampled by the kernel's angular policy.
 pub fn curve_points(curve: &PlanarCurve) -> Vec<[f64; 3]> {
-    curve.tessellate_angle(cadkernel::tessellation::DEFAULT_ANGLE)
+    curve.tessellate_angle(DISPLAY_ANGLE)
 }
 
 /// The snap candidates an entity's curve offers, in the two channels the