stop hard-coding model_id

app.py

@@ -28,8 +28,8 @@ rate_limiter = RateLimiter()
 class BasicAgent:
     def __init__(self):
         model = LiteLLMModel(
-            model_id="gemini/gemini-2.5-flash", 
-            api_key=os.getenv("GOOGLE_API_KEY")
+            model_id=os.getenv("MODEL_ID"), 
+            api_key=os.getenv("API_KEY")
         )
         self.agent = CodeAgent(
             tools=[