feat(render): double-single fills for the face3d pipeline

Table / PolyfaceMesh / greek-text / mleader-background fills go through
the face3d pipeline; their vertices were single f32 and quantized at UTM
scale. WireModel now carries a fill_tris_low residual (filled by the
tessellate Lines path), Face3DVertex gains position_low (location 3), and
face3d.wgsl reconstructs the eye-relative position from the pair. 3DFACE
quads built from key_vertices use a zero residual (no low source).

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/scene/mod.rs

@@ -8210,6 +8210,7 @@ fn tessellate_entity(
             plinegen: true,
             vp_scissor: None,
             fill_tris: vec![],
+            fill_tris_low: Vec::new(),
         };
 
         if let Some(cache) = block_cache {
@@ -8422,6 +8423,7 @@ fn tessellate_entity(
                     plinegen: true,
                     vp_scissor: None,
                     fill_tris: vec![],
+                    fill_tris_low: Vec::new(),
                 }];
             }
             if h_px < 5.0 && aabb != WireModel::UNBOUNDED_AABB {
@@ -8460,6 +8462,7 @@ fn tessellate_entity(
                     plinegen: true,
                     vp_scissor: None,
                     fill_tris,
+                    fill_tris_low: Vec::new(),
                 }];
             }
         }
@@ -8569,6 +8572,7 @@ fn lod_stub_wire(
         plinegen: true,
         vp_scissor: None,
         fill_tris: vec![],
+        fill_tris_low: Vec::new(),
     }
 }
 
@@ -8628,6 +8632,7 @@ fn lod_stub_wire_3d(
         plinegen: true,
         vp_scissor: None,
         fill_tris: vec![],
+        fill_tris_low: Vec::new(),
     }
 }