fix(agent): keep Nous GPT-5 fallback on chat completions

run_agent.py

@@ -3065,6 +3065,10 @@ class AIAgent:
     ) -> bool:
         """Return True when this provider/model pair should use Responses API."""
         normalized_provider = (provider or "").strip().lower()
+        # Nous serves GPT-5.x models via its OpenAI-compatible chat
+        # completions endpoint; its /v1/responses endpoint returns 404.
+        if normalized_provider == "nous":
+            return False
         if normalized_provider == "copilot":
             try:
                 from hermes_cli.models import _should_use_copilot_responses_api