fix(terminal): avoid lazy-loading tool manifest in async websocket handler

The container-user resolver introduced in 9f72093 accessed
'tool_type.manifest', which triggers a SQLAlchemy lazy load inside the
async WebSocket coroutine and raises MissingGreenlet. Fetch the manifest
explicitly with db_session.get() instead, matching the pattern used in
instance_service.py.

- Replace relationship access with explicit async loads in
  _resolve_container_user().
- Add unit tests covering manifest, base-definition, legacy, and missing
  manifest cases.
- Update project map artifacts.

Quality gates: pytest tests/api tests/services/test_terminal_manager_multi.py tests/unit (247 passed), ruff check (clean).

apps/api/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: apps/api
 
 ## role
-FastAPI backend API that manages projects, git repositories, development tools, and tool instances via Docker Compose
+Backend API server for the Headquarter platform, providing self-hosted project management, git repository orchestration, and development tool integration.
 ## parent
 index: apps/.pi-map.index.md
 map: apps/.pi-map.md
@@ -22,6 +22,12 @@ map: apps/.pi-map.md
 - apps/api/alembic
   index: apps/api/alembic/.pi-map.index.md
   map: apps/api/alembic/.pi-map.md
+- apps/api/app
+  index: apps/api/app/.pi-map.index.md
+  map: apps/api/app/.pi-map.md
+- apps/api/headquarter_api.egg-info
+  index: apps/api/headquarter_api.egg-info/.pi-map.index.md
+  map: apps/api/headquarter_api.egg-info/.pi-map.md
 - apps/api/src
   index: apps/api/src/.pi-map.index.md
   map: apps/api/src/.pi-map.md