feat(render): render thick and tapered analytical arcs directly on GPU

- Repurpose CircleInstance center_high.w and params.w for start_width and end_width (preserving exact 128-byte stride)
- Route wide polylines, tapered polylines with bulges, and donuts through split_mixed_polyline into GPU analytical arc instances
- Compute physical annular bands, width tapers, and round end caps in circle.wgsl using world-space distances to prevent 3D perspective foreshortening distortion
- Expand bounding quad margins dynamically with grazing-angle compensation to eliminate clipping
- Relax pick_tris check in wire classification and partition routines so wide entities retain CPU picking while drawing analytically
- Add unit and hardware GPU integration tests, including tilted 3D perspective rendering verification

src/scene/pipeline/ellipse_gpu.rs

@@ -254,7 +254,7 @@ pub fn extract_ellipse_instances(
 ) -> Option<Vec<EllipseInstance>> {
     if wire.tangent_geoms.is_empty()
         || !wire.fill_tris.is_empty()
-        || !wire.pick_tris.is_empty()
+        || wire.fill_is_3d
         || !wire.text_verts.is_empty()
         || wire.render_instance.is_some()
     {