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/scene/pipeline/face3d_gpu.rs

@@ -52,16 +52,17 @@ pub struct Face3DGpu {
 }
 
 impl Face3DGpu {
-    /// Build a batched GPU buffer from Face3D wire models.
+    /// Build a batched GPU buffer from Face3D wire models and mesh fill_tris.
     ///
-    /// Each WireModel's `key_vertices` holds the 4 corners in local space
-    /// (world_offset already applied by tessellate.rs).  Two triangles are
-    /// emitted per face: (p0,p1,p2) and (p0,p2,p3).
-    pub fn from_wires(device: &wgpu::Device, wires: &[WireModel]) -> Self {
-        let mut vertices: Vec<Face3DVertex> = Vec::with_capacity(wires.len() * 6);
+    /// - `face3d_wires`: Face3D entities — `key_vertices` holds 4 quad corners;
+    ///   emits 2 triangles per face.
+    /// - `all_wires`: all entity wires — `fill_tris` holds pre-triangulated
+    ///   fill data for PolyfaceMesh / PolygonMesh.
+    pub fn from_wires(device: &wgpu::Device, face3d_wires: &[WireModel], all_wires: &[WireModel]) -> Self {
+        let mut vertices: Vec<Face3DVertex> = Vec::with_capacity(face3d_wires.len() * 6);
 
-        for wire in wires {
-            // key_vertices has exactly 4 entries for Face3D (p0..p3).
+        // Face3D quads (4 key_vertices → 2 triangles).
+        for wire in face3d_wires {
             if wire.key_vertices.len() < 4 {
                 continue;
             }
@@ -69,17 +70,26 @@ impl Face3DGpu {
             let fill_color = [r * 0.45, g * 0.45, b * 0.45, a];
             let p = &wire.key_vertices;
             let v = |i: usize| Face3DVertex { position: p[i], color: fill_color };
-
-            // Triangle 1: p0, p1, p2
             vertices.push(v(0));
             vertices.push(v(1));
             vertices.push(v(2));
-            // Triangle 2: p0, p2, p3
             vertices.push(v(0));
             vertices.push(v(2));
             vertices.push(v(3));
         }
 
+        // PolyfaceMesh / PolygonMesh pre-triangulated fills.
+        for wire in all_wires {
+            if wire.fill_tris.is_empty() {
+                continue;
+            }
+            let [r, g, b, a] = wire.color;
+            let fill_color = [r * 0.45, g * 0.45, b * 0.45, a];
+            for &position in &wire.fill_tris {
+                vertices.push(Face3DVertex { position, color: fill_color });
+            }
+        }
+
         let vertex_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
             label: Some("face3d.vbuf"),
             contents: bytemuck::cast_slice(&vertices),

src/scene/pipeline/mod.rs

@@ -637,13 +637,15 @@ impl Pipeline {
     /// Upload all 3DFACE entities as two batched GPU objects:
     /// - `gpu_face3d_fill`: filled triangles (1 buffer, 1 draw call)
     /// - `gpu_face3d_edges`: merged edge wires (1 buffer, 1 draw call)
-    pub fn upload_face3d(&mut self, device: &wgpu::Device, face3d_wires: &[WireModel]) {
-        if face3d_wires.is_empty() {
+    pub fn upload_face3d(&mut self, device: &wgpu::Device, face3d_wires: &[WireModel], all_wires: &[WireModel]) {
+        let has_fills = !face3d_wires.is_empty()
+            || all_wires.iter().any(|w| !w.fill_tris.is_empty());
+        if !has_fills {
             self.gpu_face3d_fill = None;
             self.gpu_face3d_edges = vec![];
             return;
         }
-        self.gpu_face3d_fill = Some(Face3DGpu::from_wires(device, face3d_wires));
+        self.gpu_face3d_fill = Some(Face3DGpu::from_wires(device, face3d_wires, all_wires));
         self.gpu_face3d_edges = WireGpu::from_batch(device, face3d_wires);
     }