perf(worker): 解耦异步等待登记与跨城提交

媒体突发中的等待准入行是已同步持久化任务的可恢复派生状态，却逐条等待跨城同步提交并串行占用全局容量锁。\n\n仅对异步等待登记事务设置 synchronous_commit=off；任务实体、素材、执行准入、River job、租约、状态与账务继续同步提交。主备切换若命中极小窗口，由既有 queued-task 恢复器重建等待登记。\n\n验证：临时 PostgreSQL 18 跨 Store 分布式准入集成测试通过；Go 全量测试、go vet、gofmt 通过。

apps/api/internal/store/admission_queue.go

@@ -151,6 +151,16 @@ func (s *Store) queueTaskAdmissionOnce(
 		return TaskAdmission{}, err
 	}
 	defer rollbackTransaction(tx)
+	// The task itself was synchronously committed before this derived FIFO
+	// registration. Do not serialize a large media burst on one cross-region
+	// synchronous commit per waiting row: PostgreSQL still writes this WAL
+	// locally, and generic queued-task recovery reconstructs a registration
+	// after failover if the small asynchronous-commit window is hit. Admission,
+	// River job, execution lease, task state, and billing commits stay fully
+	// synchronous.
+	if _, err := tx.Exec(ctx, `SET LOCAL synchronous_commit = off`); err != nil {
+		return TaskAdmission{}, err
+	}
 
 	if err := tryAdmissionTransactionLock(ctx, tx, "task-admission:"+input.TaskID); err != nil {
 		return TaskAdmission{}, err