Add support for OAuth-based authentication with access/refresh tokens
and expiration tracking for API keys. Extend provider groups with
static headers configuration and headers profile options.
Changes include:
- Add AccessToken, RefreshToken, ExpiresAt, AccountID, ProjectID to APIKey model
- Add StaticHeaders and HeadersProfile to ProviderGroup model
- Add TokenRefresh configuration for background token management
- Support new provider types: ClaudeCode, Codex, GeminiCLI, Antigravity
- Update sync service to include new fields in provider snapshots
- Introduce `SyncOutboxService` and model to retry failed CP-to-Redis sync operations
- Update `SyncService` to handle sync failures by enqueuing tasks to the outbox
- Centralize provider group and API key validation logic into `ProviderGroupManager`
- Refactor API handlers to utilize the new manager and robust sync methods
- Add configuration options for sync outbox (interval, batch size, retries)
