fix: envvar name for nebius

app.py

@@ -48,7 +48,7 @@ async def chat_logic(
 
         # Set environment variables for the current process.
         os.environ["GITHUB_REPO"] = github_repo
-        os.environ["HUGGINGFACE_API_KEY"] = hf_token
+        os.environ["NEBIUS_API_KEY"] = hf_token
 
         # Asynchronously initialize the graph and store it in the session state
         # to reuse it for subsequent messages in the same session.