fix(viewcube): cache UCS picker names behind an epoch

The two per-frame ViewCube blocks rebuilt the named-UCS name list (N String clones plus a Vec) every frame; now Scene::cached_ucs_names memoises it behind ucs_epoch and the picker takes the Arc, so frames cost a refcount bump. Bumped on UCS SAVE, UCS DELETE, RENAME UCS, record-API ucss patch, file-open, and undo Full-swap. Tests: cached_ucs_names_returns_same_arc_until_bump pins the hit path; cached_ucs_names_invalidated_by_bump pins rebuild with new content. Full suite: 1976 passed / 0 failed / 25 ignored.

src/app/record_api.rs

@@ -1611,7 +1611,12 @@ impl OpenCADStudio {
                     "app_ids" => patch_table!(app_ids),
                     "views" => patch_table!(views),
                     "vports" => patch_table!(vports),
-                    "ucss" => patch_table!(ucss),
+                    "ucss" => {
+                        patch_table!(ucss);
+                        if changed {
+                            self.tabs[i].scene.bump_ucs_epoch();
+                        }
+                    }
                     "vx_table" => patch_table!(vx_table),
                     _ => unreachable!(),
                 }