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/api/tests/unit/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: apps/api/tests/unit
 
 ## role
-Unit test suite for the API backend, covering configuration, Docker services, git operations, file handling, health monitoring, notifications, permissions, and lifecycle management.
+Unit test suite for the API backend, covering configuration, Docker operations, Git services, file handling, health monitoring, notifications, and SSH key management.
 ## parent
 index: apps/api/tests/.pi-map.index.md
 map: apps/api/tests/.pi-map.md
@@ -18,6 +18,7 @@ map: apps/api/tests/.pi-map.md
 - test_file_service.py
 - test_git_mount_resolution.py
 - test_git_mounts.py
+- test_git_operations.py
 - test_git_repository_clone_preflight.py
 - test_git_repository_working_clones.py
 - test_git_service.py
@@ -32,9 +33,7 @@ map: apps/api/tests/.pi-map.md
 - test_notifications_api_routes.py
 - test_permission_fixer.py
 - test_readiness_probe.py
-- test_session_branch_selection.py
 - test_ssh_keys.py
-- test_tool_instances_legacy.py
 ## links
 index: apps/api/tests/unit/.pi-map.index.md
 map: apps/api/tests/unit/.pi-map.md