Update alphaear skills to use MiniMax as default LLM

Changes:
- Added 'minimax' provider to LLM factory
- Changed default LLM_PROVIDER from 'ust' to 'minimax'
- Changed default LLM_MODEL from 'Qwen' to 'MiniMax-Text-01'
- Updated REASONING_MODEL_PROVIDER and TOOL_MODEL_PROVIDER to minimax
- Sentiment tools now prefer MINIMAX_API_KEY over UST_KEY_API
- .env.example updated with MiniMax defaults

skills/alphaear-sentiment/scripts/llm/capability.py

@@ -77,7 +77,7 @@ if __name__ == "__main__":
     load_dotenv(os.path.expanduser("~/.config/opencode/.env"))
 
     # 测试当前配置的模型
-    p = os.getenv("LLM_PROVIDER", "ust")
+    p = os.getenv("LLM_PROVIDER", "minimax")
     m = os.getenv("LLM_MODEL", "Qwen")
 
     print(f"Testing {p}/{m}...")