fix: cleanup Qwen OAuth provider gaps

- Add HERMES_QWEN_BASE_URL to OPTIONAL_ENV_VARS in config.py (was missing
  despite being referenced in code)
- Remove redundant qwen-oauth entry from _API_KEY_PROVIDER_AUX_MODELS
  (non-aggregator providers use their main model for aux tasks automatically)

agent/auxiliary_client.py

@@ -106,7 +106,6 @@ _API_KEY_PROVIDER_AUX_MODELS: Dict[str, str] = {
     "opencode-zen": "gemini-3-flash",
     "opencode-go": "glm-5",
     "kilocode": "google/gemini-3-flash-preview",
-    "qwen-oauth": "qwen3-coder",
 }
 
 # OpenRouter app attribution headers