Update default model to gemma

routers/gemini.py

@@ -19,7 +19,7 @@ client = genai.Client(api_key=gemini_key)
 ALLOWED_CHAT_MODELS = ("gemini-flash-latest", "gemma-4-26b-a4b-it")
 
 # Default text-chat model. Override with GEMINI_CHAT_MODEL env var (must be one of ALLOWED_CHAT_MODELS).
-GEMINI_DEFAULT_CHAT_MODEL = os.environ.get("GEMINI_CHAT_MODEL", "gemini-flash-latest")
+GEMINI_DEFAULT_CHAT_MODEL = os.environ.get("GEMINI_CHAT_MODEL", "gemma-4-26b-a4b-it")
 if GEMINI_DEFAULT_CHAT_MODEL not in ALLOWED_CHAT_MODELS:
     raise RuntimeError(
         f"GEMINI_CHAT_MODEL must be one of {list(ALLOWED_CHAT_MODELS)}, got '{GEMINI_DEFAULT_CHAT_MODEL}'."