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/integration/test_workspaces_api.py

@@ -8,12 +8,14 @@ import pytest
 from fastapi.testclient import TestClient
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from src.models.git_repository import GitRepository
-from src.models.project import Project
-from src.models.tool_instance import ToolInstance
-from src.models.tool_type import ToolType
-from src.models.workspace import Workspace
-from src.services.workspace_manager import WorkspaceManager
+from src.models import (
+    GitRepository,
+    Project,
+    ToolInstance,
+    ToolType,
+    Workspace,
+)
+from src.services.shared.workspace_manager import WorkspaceManager
 
 
 def _get_user_id_from_client(client: TestClient) -> uuid.UUID: