feat: complete workspace-first-ui cleanup and tests

- Delete dead repo-workspace code: RepoWorkspacePage, useRepoWorkspace,
  WorkspaceLayout, FileBrowser, old git components (git-toolbar, file-editor,
  commit-panel), and repo-workspace.css.
- Fix stale backend test imports for moved models/services.
- Add GitOperations unit tests.
- Add integration tests for workspace files, git, and instances endpoints.
- Add frontend tests for WorkspaceDetailPage and ProjectCard.
- Update OpenSpec workspace-first-ui tasks and mark change completed.
- Regenerate project maps.

Quality gates: npm run typecheck, npm run lint, npm test -- --run (87 passed),
python3 -m py_compile on changed backend files, pytest backend workspace tests.

openspec/changes/workspace-first-ui/.pi-map.index.md

@@ -1,21 +1,22 @@
-# workspace-first-ui (index)
-dir: workspace-first-ui
+# openspec/changes/workspace-first-ui (index)
+dir: openspec/changes/workspace-first-ui
 
 ## role
-Design and planning documentation for a workspace-first UI refresh that restructures the application around persistent writable workspaces rather than direct repository browsing.
+Product specification and design documentation package for a workspace-first UI refresh project that reorients the application around persistent writable workspaces rather than direct repository browsing.
 ## parent
-index: ./.pi-map.index.md
-map: ./.pi-map.md
+index: openspec/changes/.pi-map.index.md
+map: openspec/changes/.pi-map.md
 ## children
 -
 ## files
+- .openspec.yaml
 - design.md
 - proposal.md
 - spec.md
 - tasks.md
 ## links
-index: workspace-first-ui/.pi-map.index.md
-map: workspace-first-ui/.pi-map.md
+index: openspec/changes/workspace-first-ui/.pi-map.index.md
+map: openspec/changes/workspace-first-ui/.pi-map.md
 ## workflows
 -
 ## dirty