chore: update model lists, bump to v0.2.1, fix package build

- OpenAI: add GPT-5.4, GPT-5.4 Pro; remove o-series and legacy GPT-4o
- Anthropic: add Claude Opus 4.6, Sonnet 4.6; remove legacy 4.1/4.0/3.x
- Google: add Gemini 3.1 Pro, 3.1 Flash Lite; remove deprecated
  gemini-3-pro-preview and Gemini 2.0 series
- xAI: clean up model list to match current API
- Simplify UnifiedChatOpenAI GPT-5 temperature handling
- Add missing tradingagents/__init__.py (fixes pip install building)

tradingagents/llm_clients/openai_client.py

@@ -8,25 +8,23 @@ from .validators import validate_model
 
 
 class UnifiedChatOpenAI(ChatOpenAI):
-    """ChatOpenAI subclass that strips incompatible params for certain models."""
+    """ChatOpenAI subclass that strips temperature/top_p for GPT-5 family models.
+
+    GPT-5 family models use reasoning natively. temperature/top_p are only
+    accepted when reasoning.effort is 'none'; with any other effort level
+    (or for older GPT-5/GPT-5-mini/GPT-5-nano which always reason) the API
+    rejects these params. Langchain defaults temperature=0.7, so we must
+    strip it to avoid errors.
+
+    Non-GPT-5 models (GPT-4.1, xAI, Ollama, etc.) are unaffected.
+    """
 
     def __init__(self, **kwargs):
-        model = kwargs.get("model", "")
-        if self._is_reasoning_model(model):
+        if "gpt-5" in kwargs.get("model", "").lower():
             kwargs.pop("temperature", None)
             kwargs.pop("top_p", None)
         super().__init__(**kwargs)
 
-    @staticmethod
-    def _is_reasoning_model(model: str) -> bool:
-        """Check if model is a reasoning model that doesn't support temperature."""
-        model_lower = model.lower()
-        return (
-            model_lower.startswith("o1")
-            or model_lower.startswith("o3")
-            or "gpt-5" in model_lower
-        )
-
 
 class OpenAIClient(BaseLLMClient):
     """Client for OpenAI, Ollama, OpenRouter, and xAI providers."""