refactor: migrate from create_react_agent to create_deep_agent

- Replace langgraph create_react_agent with deepagents create_deep_agent
- Sub-agents now configured as SubAgent dicts dispatched via built-in task tool
- Stream filter updated: langgraph_node 'agent' → 'model'
- Accept both AIMessage and AIMessageChunk in stream filter
- Collector only captures write mutations (insert/update/delete)
- Add deepagents>=0.4.10 to requirements.txt

app/core/ws_context.py

@@ -91,10 +91,10 @@ async def execute_on_client(
     else:
         logger.info("execute_on_client: got result type=%s keys=%s", type(result).__name__, list(result.keys()) if isinstance(result, dict) else "N/A")
     collector = _tool_result_collector.get(None)
-    if collector is not None:
+    if collector is not None and action in ("insert", "update", "delete"):
         collector.append({
             "action": action,
             "table": table,
-            "data": result,
+            "data": data or {},
         })
     return result