feat(core): implement sync outbox mechanism and refactor provider validation

- 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)

internal/api/handler.go

@@ -22,6 +22,7 @@ type Handler struct {
 	rdb            *redis.Client
 	logWebhook     *service.LogWebhookService
 	logPartitioner *service.LogPartitioner
+	groupManager   *service.ProviderGroupManager
 }
 
 func NewHandler(db *gorm.DB, logDB *gorm.DB, sync *service.SyncService, logger *service.LogWriter, rdb *redis.Client, partitioner *service.LogPartitioner) *Handler {
@@ -36,6 +37,7 @@ func NewHandler(db *gorm.DB, logDB *gorm.DB, sync *service.SyncService, logger *
 		rdb:            rdb,
 		logWebhook:     service.NewLogWebhookService(rdb),
 		logPartitioner: partitioner,
+		groupManager:   service.NewProviderGroupManager(),
 	}
 }