refactor: replace orchestrator with LangGraph deep-agent supervisors

- Add app/core/deep_agent.py with Home and Floating supervisor graphs
  using LangGraph create_react_agent (hierarchical pattern)
- Strip ChatAgent classes from all 4 agent files, keep @tool functions
- Rewrite output_formatter.py for event-based (token/tool_end/mutations) stream
- Update device_ws.py to use run_home_stream/run_floating_stream
- Rewrite chat.py REST route to use run_home
- Add update_core_memory tool to both supervisors
- Add langgraph>=0.3.0 to requirements.txt
- Remove orchestrator.py, execution_plan.py, agent_registry.py, plans.py
- Remove PlanAction, PlanStep, ExecutionPlan, execution_mode from schemas
- Update all affected tests to match new API
- Remove 6 deprecated test files for deleted modules
- Clean up stale docstrings referencing removed orchestrator

tests/test_memory_middleware.py

@@ -250,15 +250,15 @@ def test_home_request_calls_memory_middleware(client):
     token = make_jwt("power", user_id=USER_ID)
     session_id = str(uuid.uuid4())
 
-    async def _mock_stream(user_id, message, context, reg=None):
+    async def _mock_stream(user_id, message, context, db_session_factory=None):
         # Verify memory context was injected
         assert context.get("core_memory") == {"tz": "UTC"}
-        yield "task_agent", ""
-        yield "task_agent", '{"type": "text", "content": "Done"}'
+        yield ("token", "Done")
+        yield ("mutations", [])
 
     with (
         patch("app.api.routes.device_ws.MemoryMiddleware", _MockMiddleware),
-        patch("app.api.routes.device_ws.orchestrate_v3_stream", side_effect=_mock_stream),
+        patch("app.api.routes.device_ws.run_home_stream", side_effect=_mock_stream),
     ):
         with client.websocket_connect(f"/api/v1/ws/device?token={token}") as ws:
             ws.send_text(json.dumps({