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/handlers/chat.py

@@ -7,8 +7,8 @@ import structlog
 from nio.api import RoomVisibility
 from nio.responses import RoomCreateError
 
+from adapter.matrix.agent_registry import AgentRegistry
 from adapter.matrix.store import (
-    get_selected_agent_id,
     get_user_meta,
     next_chat_id,
     next_platform_chat_id,
@@ -49,6 +49,7 @@ async def _fallback_new_chat(
 def make_handle_new_chat(
     client: Any | None,
     store: Any | None,
+    registry: AgentRegistry | None = None,
 ) -> Callable[..., Awaitable[list]]:
     async def handle_new_chat(
         event: IncomingCommand, auth_mgr, platform, chat_mgr, settings_mgr
@@ -105,7 +106,12 @@ def make_handle_new_chat(
             state_key=room_id,
         )
 
-        selected_agent_id = await get_selected_agent_id(store, event.user_id)
+        agent_id = None
+        if registry is not None:
+            agent_id = registry.get_agent_id_for_user(event.user_id)
+            if agent_id is None and registry.agents:
+                agent_id = registry.agents[0].agent_id
+
         room_meta: dict = {
             "room_type": "chat",
             "chat_id": chat_id,
@@ -113,9 +119,8 @@ def make_handle_new_chat(
             "matrix_user_id": event.user_id,
             "space_id": space_id,
             "platform_chat_id": platform_chat_id,
+            "agent_id": agent_id,
         }
-        if selected_agent_id:
-            room_meta["agent_id"] = selected_agent_id
         await set_room_meta(store, room_id, room_meta)
         ctx = await chat_mgr.get_or_create(
             user_id=event.user_id,