fix: default LLM to HF Router + Qwen2.5-72B, no custom Space variables needed

backend/env/sql_env.py

@@ -70,11 +70,11 @@ class RewardInfo(BaseModel):
 def _make_client() -> AsyncOpenAI:
     return AsyncOpenAI(
         api_key=os.environ.get("HF_TOKEN", ""),
-        base_url=os.environ.get("API_BASE_URL", "https://api.openai.com/v1"),
+        base_url=os.environ.get("API_BASE_URL", "https://router.huggingface.co/v1"),
     )
 
 
-_MODEL = os.environ.get("MODEL_NAME", "gpt-4o-mini")
+_MODEL = os.environ.get("MODEL_NAME", "Qwen/Qwen2.5-72B-Instruct")
 
 BASE_SYSTEM_PROMPT = """You are a SQL expert. Given a natural language question and a SQLite database schema, write a correct SQL query.