Feat: hatch boundary grip editing — all edge types supported

Polyline, Line, CircularArc, EllipticArc, and Spline boundary edges
all get diamond grips at their control vertices. Dragging a grip updates
the underlying DXF boundary vertex and immediately rebuilds the GPU
hatch model via Scene::apply_grip.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scene/mod.rs

@@ -1660,6 +1660,15 @@ impl Scene {
         if let Some(entity) = self.document.get_entity_mut(handle) {
             dispatch::apply_grip(entity, grip_id, apply);
         }
+        // Rebuild the GPU hatch model when a hatch boundary vertex moves.
+        if let Some(EntityType::Hatch(dxf)) = self.document.get_entity(handle) {
+            let color = tessellate::aci_to_rgba(&dxf.common.color);
+            if let Some(model) = Self::hatch_model_from_dxf(dxf, color) {
+                self.hatches.insert(handle, model);
+            } else {
+                self.hatches.remove(&handle);
+            }
+        }
     }
 
     // ── Hit-test convenience: wire name → Handle ──────────────────────────