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.

apps/web/src/pages/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: apps/web/src/pages
 
 ## role
-Implements the complete set of top-level routed page components for the web application, covering all major user-facing features including project management, git operations, workspace management, terminal access, user settings, and system administration.
+Contains all top-level page components that serve as route endpoints for the web application's main navigation areas, each handling a distinct functional domain of the development environment platform.
 ## parent
 index: apps/web/src/.pi-map.index.md
 map: apps/web/src/.pi-map.md
@@ -19,12 +19,12 @@ map: apps/web/src/.pi-map.md
 - ProjectSettingsPage.tsx
 - ProjectsPage.test.tsx
 - ProjectsPage.tsx
-- RepoWorkspacePage.tsx
 - SessionsPage.tsx
 - SettingsPage.tsx
 - SshKeysPage.tsx
 - TerminalPage.tsx
 - ToolWorkshopPage.tsx
+- WorkspaceDetailPage.test.tsx
 - WorkspaceDetailPage.tsx
 - WorkspacesPage.tsx
 ## links
@@ -34,6 +34,6 @@ map: apps/web/src/pages/.pi-map.md
 - change pages behavior
   read: ConfigProfilesPage.tsx, DashboardPage.tsx, GitHistoryPage.tsx
 - update pages tests
-  read: DashboardPage.test.tsx, ProjectsPage.test.tsx
+  read: DashboardPage.test.tsx, ProjectsPage.test.tsx, WorkspaceDetailPage.test.tsx
 ## dirty
 -