Feat: add GPT-5.1, GPT‑5.1 Instant and Claude-Opus-4.5 (#11559)

### What problem does this PR solve?

Add GPT-5.1, GPT‑5.1 Instant and Claude-Opus-4.5. #11548

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/llm/chat_model.py

@@ -132,6 +132,11 @@ class Base(ABC):
 
         gen_conf = {k: v for k, v in gen_conf.items() if k in allowed_conf}
 
+        model_name_lower = (self.model_name or "").lower()
+        # gpt-5 and gpt-5.1 endpoints have inconsistent parameter support, clear custom generation params to prevent unexpected issues
+        if "gpt-5" in model_name_lower:
+            gen_conf = {}
+
         return gen_conf
 
     def _chat(self, history, gen_conf, **kwargs):