fix(api): remove unsupported 'user' param from FC/ReAct invoke_llm calls

FunctionCallStrategy and ReActStrategy were passing user=self.context.user_id
to ModelInstance.invoke_llm() which doesn't accept that parameter.
This caused tool-using agent runs to fail with:
  "ModelInstance.invoke_llm() got an unexpected keyword argument 'user'"

Verified: Agent V2 with current_time tool now works end-to-end:
  ROUND 1: LLM thought -> CALL current_time -> got time
  ROUND 2: LLM generates answer with time info
Made-with: Cursor

api/core/agent/patterns/function_call.py

@@ -92,7 +92,6 @@ class FunctionCallStrategy(AgentPattern):
                 tools=current_tools,
                 stop=stop,
                 stream=stream,
-                user=self.context.user_id,
                 callbacks=[],
             )
 

api/core/agent/patterns/react.py

@@ -114,7 +114,6 @@ class ReActStrategy(AgentPattern):
                 model_parameters=model_parameters,
                 stop=stop,
                 stream=stream,
-                user=self.context.user_id or "",
                 callbacks=[],
             )