close#16132
## Summary
This PR completes the Go-side merge and cleanup for chat channel APIs,
including handler/service wiring, route registration, and test coverage.
Implemented and aligned 5 chat channel APIs:
```
- POST `/api/v1/chat-channels`
- GET `/api/v1/chat-channels`
- GET `/api/v1/chat-channels/:channel_id`
- PATCH `/api/v1/chat-channels/:channel_id`
- DELETE `/api/v1/chat-channels/:channel_id`
```
Co-authored-by: Haruko386 <tryeverypossible@163.com>