Feat: Phase 4.1/4.2 — Polyline, Polyline2D, Polyline3D, Ray, XLine render and grips

- polyline.rs: TruckConvertible/Grippable/PropertyEditable/Transformable
  for all three polyline types; Polyline2D handles bulge arcs via the
  same truck Wire path as LwPolyline; Polyline and Polyline3D use
  TruckObject::Lines for straight-segment rendering
- ray.rs: Ray renders as base→+1e6; XLine renders as ±1e6; both have
  base-point and direction grips; mirror correctly reflects direction
  vector; base X/Y/Z and Dir X/Y/Z exposed in properties panel
- traits.rs: dispatch all five new entity types through
  to_truck_entity, grips, geometry_properties, apply_geom_prop,
  apply_grip, apply_transform

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

src/entities/mod.rs

@@ -11,6 +11,8 @@ pub mod multileader;
 pub mod lwpolyline;
 pub mod mtext;
 pub mod point;
+pub mod polyline;
+pub mod ray;
 pub mod spline;
 pub mod text;
 mod text_support;