feat(api): add unified Models API endpoint

- Add models_service.py with model query logic and caching
- Add models.py unified endpoint supporting Claude/OpenAI/Gemini formats
- Auto-detect API format based on request headers
- Support /v1/models and /v1beta/models (Gemini) paths
- Update route registration and comments

src/api/public/claude.py

@@ -3,6 +3,8 @@ Claude API 端点
 
 - /v1/messages - Claude Messages API
 - /v1/messages/count_tokens - Token Count API
+
+注意: /v1/models 端点由 models.py 统一处理，根据请求头返回对应格式
 """
 
 from fastapi import APIRouter, Depends, Request