fix: correct polyline arc direction, text precision, Face3D edge color, buffer chunking

- fix: polyline arc center sign was inverted (- → +) causing arcs to render on the
  wrong side in LwPolyline and Polyline2D
- fix: store glyph strokes in local space with f64 origin so world_offset subtraction
  uses f64 precision; prevents blocky text at large UTM coordinates
- fix: Face3D fill darkened to 45% so edge wires are visually distinct from fill
- fix: wire batch vertex buffer chunked to 256 MB GPU limit (was panic on large files)
- fix: gpu_face3d_edges changed from Option<WireGpu> to Vec<WireGpu> to support chunks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scene/pipeline/face3d_gpu.rs

@@ -65,9 +65,10 @@ impl Face3DGpu {
             if wire.key_vertices.len() < 4 {
                 continue;
             }
-            let color = wire.color;
+            let [r, g, b, a] = wire.color;
+            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 };
+            let v = |i: usize| Face3DVertex { position: p[i], color: fill_color };
 
             // Triangle 1: p0, p1, p2
             vertices.push(v(0));