fix(render): UTM-precise UCS icon + fallback outlines (hatch etc.)

Two UTM-scale rendering defects.

- UCS icon jittered: it projects only axis DIRECTIONS but went through the
  full view_proj, whose ~5.7e6 translation cancels catastrophically in f32.
  Feed it the rotation-only view_proj_rte instead (translation dropped).

- Fallback outline geometry (hatch boundary, viewport/insert/ole2frame
  frames, Solid3D edge wires) built absolute f32 points with an empty
  points_low, so at UTM the outline sat ~0.5 m off its own fill (the hatch
  fill renders precisely via the world_origin-relative HatchModel pipeline).
  FallbackGeometry now carries absolute f64 points + key vertices; the
  tessellate dispatcher splits them into the double-single high/low pair the
  relative-to-eye wire pass needs, so outlines land exactly on their fills.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/view.rs

@@ -167,7 +167,11 @@ impl OpenCADStudio {
                 let cam = tab.scene.camera.borrow();
                 let (_, ux, uy, uz) = tab.ucs_xform().axes();
                 Some(overlay::UcsIconParams {
-                    view_proj: cam.view_proj(vp_bounds),
+                    // Rotation-only projection: the icon shows axis DIRECTIONS
+                    // only, so the full view_proj's huge UTM translation would
+                    // just cancel catastrophically in f32 and make the tripod
+                    // jitter. view_proj_rte drops the translation. (#utm-ucs)
+                    view_proj: cam.view_proj_rte(vp_bounds),
                     bounds: vp_bounds,
                     axes: (ux, uy, uz),
                 })