Add type hint to /chat messages parameter (gradio requires typed API params)

app.py

@@ -129,8 +129,8 @@ app = Server()
 
 
 @app.api()
-def chat(messages, reasoning: bool = True) -> Iterator[dict]:
-    """Reasoning-aware chat endpoint. Takes `messages` (JSON-encoded list of
+def chat(messages: list, reasoning: bool = True) -> Iterator[dict]:
+    """Reasoning-aware chat endpoint. Takes `messages` (list of
     role/content/reasoning_details dicts) and an optional `reasoning` bool.
     Streams `{"event":"delta","text":...}` lines, then a final `done` event
     with the new assistant message so the frontend can persist it."""