Restructure the task relay system for better separation of concerns:
- Extract task billing into service/task_billing.go with unified settlement flow
- Move task polling loop from controller to service/task_polling.go (supports Suno + video platforms)
- Split RelayTask into fetch/submit paths with dedicated retry logic (taskSubmitWithRetry)
- Add TaskDto, TaskResponse generics, and FetchReq to dto/task.go
- Add taskcommon/helpers.go for shared task adaptor utilities
- Remove controller/task_video.go (logic consolidated into service layer)
- Update all task adaptors (ali, doubao, gemini, hailuo, jimeng, kling, sora, suno, vertex, vidu)
- Simplify frontend task logs to use new TaskDto response format
The i18n middleware runs before UserAuth, so user settings weren't
available when language was detected. Now GetLangFromContext checks
user settings first (set by UserAuth) before falling back to the
language set by middleware or Accept-Language header.
- Updated TokenAuth middleware to handle requests for both `/v1beta/models/` and `/v1/models/`.
- Adjusted distributor middleware to recognize the new model path.
- Enhanced relay mode determination to include the new model path.
- Added route for handling POST requests to `/models/*path`.
These changes ensure compatibility with the new model API structure, improving the overall routing and authentication flow.
- Add new context keys for user-related information
- Modify user cache and authentication middleware to populate context
- Refactor quota and notification services to use context-based user data
- Remove redundant database queries by leveraging context information
- Update various components to use new context-based user retrieval methods
