feat: workspace-first UI refresh - PR-1 backend endpoints
- Add FileService for workspace-scoped file operations
- Add GitOperations service for workspace-scoped git commands
- Add workspace_files API: GET/POST /workspaces/{id}/files
- Add workspace_git API: status, branches, commit, push, pull, fetch, checkout, history
- Add workspace_instances API: list instances per workspace
- Add top-level POST /workspaces/ (accepts repo_id directly)
- Enrich GET /projects/ with nested repositories and workspaces
- Register all new routers in main.py
- 23 tests passing (17 existing + 6 new)
Quality gates: ruff clean
alex
e7587ca9f5