fix: pass tool name as positional arg to @tool decorator

The langchain @tool decorator expects the name as the first positional
argument (name_or_callable), not as name= keyword argument.

app/core/deep_agent.py

@@ -111,7 +111,7 @@ def _build_subagent_tool(
         name=name,
     )
 
-    @tool(name=name, description=description)
+    @tool(name, description=description)
     async def _run(query: str) -> str:
         result = await subgraph.ainvoke(
             {"messages": [HumanMessage(content=query)]}