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/agent_registry.py

@@ -18,9 +18,14 @@ class AgentDefinition:
 
 
 class AgentRegistry:
-    def __init__(self, agents: list[AgentDefinition]) -> None:
+    def __init__(
+        self,
+        agents: list[AgentDefinition],
+        user_agents: Mapping[str, str] | None = None,
+    ) -> None:
         self.agents = tuple(agents)
         self._by_id = {agent.agent_id: agent for agent in self.agents}
+        self._user_agents: dict[str, str] = dict(user_agents or {})
 
     def get(self, agent_id: str) -> AgentDefinition:
         try:
@@ -28,6 +33,9 @@ class AgentRegistry:
         except KeyError as exc:
             raise AgentRegistryError(f"unknown agent id: {agent_id}") from exc
 
+    def get_agent_id_for_user(self, matrix_user_id: str) -> str | None:
+        return self._user_agents.get(matrix_user_id)
+
 
 def _required_text(entry: Mapping[str, object], key: str) -> str:
     value = entry.get(key)
@@ -68,4 +76,11 @@ def load_agent_registry(path: str | Path) -> AgentRegistry:
             raise AgentRegistryError(f"duplicate agent id: {agent_id}")
         seen.add(agent_id)
         agents.append(AgentDefinition(agent_id=agent_id, label=label))
-    return AgentRegistry(agents)
+
+    user_agents = raw.get("user_agents")
+    if user_agents is not None:
+        if not isinstance(user_agents, Mapping):
+            raise AgentRegistryError("user_agents must be a mapping of user_id to agent_id")
+        user_agents = {str(k): str(v) for k, v in user_agents.items()}
+
+    return AgentRegistry(agents, user_agents)