Update agent graph orchestration prompts

Refresh the agent graph state and prompt wiring so the newer backend and
frontend orchestration features share the same execution model. This
keeps the remaining agent-side changes aligned with the rest of the
batch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/agents/state.py

@@ -82,6 +82,9 @@ class AgentState(TypedDict):
     # Memory context (injected at start of each conversation)
     memory_context: str | None
 
+    # User LLM config (for using user-configured models)
+    user_llm_config: dict | None
+
 
 def initial_state(user_id: str, conversation_id: str) -> AgentState:
     return AgentState(
@@ -102,4 +105,5 @@ def initial_state(user_id: str, conversation_id: str) -> AgentState:
         final_response=None,
         should_respond=True,
         memory_context=None,
+        user_llm_config=None,
     )