feat(render): solid fill for PolyfaceMesh and PolygonMesh entities

PolyfaceMesh and PolygonMesh were wireframe-only. They now render with
the same flat-color solid fill as Face3D entities.

- Add fill_tris: Vec<[f32;3]> to TruckEntity and WireModel
- PolyfaceMesh: fan-triangulate each face into fill_tris
- PolygonMesh: triangulate each grid quad into fill_tris
- tessellate.rs Lines branch: apply world_offset to fill_tris
- Face3DGpu::from_wires: collect fill_tris from all wires in addition
  to Face3D key_vertices quads
- upload_face3d: pass all_wires so fill_tris are batched into one draw call

src/app/update.rs

@@ -1376,6 +1376,7 @@ impl H7CAD {
                                     aabb: crate::scene::WireModel::UNBOUNDED_AABB,
                                     plinegen: true,
             vp_scissor: None,
+            fill_tris: vec![],
                                 };
                                 previews.push(guide);
                             }