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 <noreply@anthropic.com>

src/modules/annotate/dim_continue.rs

@@ -149,6 +149,7 @@ impl CadCommand for DimContinueCommand {
             plinegen: true,
             vp_scissor: None,
             fill_tris: vec![],
+            fill_tris_low: Vec::new(),
         })
     }
 }