fix: Add missing Field import from pydantic

Fixed NameError in ChatResponse model by adding Field to pydantic imports.
This resolves deployment error on Hugging Face Spaces.

api_routes_v2.py

@@ -402,7 +402,7 @@
 
 from fastapi import APIRouter, HTTPException, UploadFile, File, Request, Form
 from fastapi.responses import StreamingResponse
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import Optional, List, Dict, Any, Generator, Callable, Tuple
 import json
 import os