chore(llm): add latest models and default to GPT-5.5

Add Claude Opus 4.8, Gemini 3.5 Flash, Grok 4.3, and Qwen3.7-Max; default
deep model is now GPT-5.5.

tradingagents/default_config.py

@@ -53,7 +53,7 @@ DEFAULT_CONFIG = _apply_env_overrides({
     "memory_log_max_entries": None,
     # LLM settings
     "llm_provider": "openai",
-    "deep_think_llm": "gpt-5.4",
+    "deep_think_llm": "gpt-5.5",
     "quick_think_llm": "gpt-5.4-mini",
     # When None, each provider's client falls back to its own default endpoint
     # (api.openai.com for OpenAI, generativelanguage.googleapis.com for Gemini, ...).