refactor(task): extract billing and polling logic from controller to service layer

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

service/billing_session.go

@@ -193,6 +193,11 @@ func (s *BillingSession) preConsume(c *gin.Context, quota int) *types.NewAPIErro
 
 // shouldTrust 统一信任额度检查，适用于钱包和订阅。
 func (s *BillingSession) shouldTrust(c *gin.Context) bool {
+	// 异步任务（ForcePreConsume=true）必须预扣全额，不允许信任旁路
+	if s.relayInfo.ForcePreConsume {
+		return false
+	}
+
 	trustQuota := common.GetTrustQuota()
 	if trustQuota <= 0 {
 		return false