feat(deploy): platform handoff — agent routing, persistence, docs cleanup

Agent routing:
- Remove !agent command and manual agent selection flow
- Registry auto-assigns agent from user_agents mapping (fallback: agents[0])
- provision_workspace_chat and !new both write agent_id to room_meta
- Reconciliation backfills agent_id from registry on cold start
- Fix duplicate agent_id block in auth.py

Deployment stability:
- Add bot-state named volume to persist lambda_matrix.db and matrix_store
- Fix docker-compose.prod.yml duplicate environment: key (was silently losing all Matrix credentials)
- Fix MATRIX_AGENT_REGISTRY_PATH to use absolute container path /app/config/...
- Add bot-state volume declaration to docker-compose.fullstack.yml

Docs and config:
- Rewrite README.md for platform handoff (deploy table, working commands only)
- Rewrite docs/matrix-prototype.md (remove stale commands and mock descriptions)
- Remove !save/!load/!context/!agent from help text and welcome message
- Add !clear, !list, !remove, !yes/!no to help text
- Clean up .env.example (remove Telegram token, internal vars, real URLs)
- Update config/matrix-agents.example.yaml with user_agents section and comments
- Add explanatory comment to Dockerfile for --ignore-requires-python
- Remove silent uv sync fallbacks in Dockerfile

adapter/matrix/store.py

@@ -45,21 +45,6 @@ async def set_user_meta(store: StateStore, matrix_user_id: str, meta: dict) -> N
     await store.set(f"{USER_META_PREFIX}{matrix_user_id}", meta)
 
 
-async def get_selected_agent_id(store: StateStore, matrix_user_id: str) -> str | None:
-    meta = await get_user_meta(store, matrix_user_id)
-    return meta.get("selected_agent_id") if meta else None
-
-
-async def set_selected_agent_id(
-    store: StateStore,
-    matrix_user_id: str,
-    agent_id: str,
-) -> None:
-    meta = dict(await get_user_meta(store, matrix_user_id) or {})
-    meta["selected_agent_id"] = agent_id
-    await set_user_meta(store, matrix_user_id, meta)
-
-
 async def set_room_agent_id(store: StateStore, room_id: str, agent_id: str) -> None:
     meta = dict(await get_room_meta(store, room_id) or {})
     meta["agent_id"] = agent_id