fix(worker): 防止事务泄漏并恢复滞留队列

为 PostgreSQL 连接增加可配置的事务空闲与锁等待超时，并在请求取消或 Worker 退出后使用独立有界上下文回滚事务。\n\n恢复过期任务时按批次使用 SKIP LOCKED，周期重建缺失或终态 River Job；锁等待超时只在确认尚未提交上游时安全重排，避免重复执行和重复结算。\n\n验证：完整 Go 测试、go vet、生产 Kustomize 渲染、gofmt 与 git diff --check 均通过。

apps/api/internal/store/billing_settlements.go

@@ -157,7 +157,7 @@ RETURNING outbox.id::text, outbox.task_id::text, outbox.action, outbox.amount::t
 }
 
 func (s *Store) ProcessBillingSettlement(ctx context.Context, settlement BillingSettlement) error {
-	return pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+	return s.beginTransaction(ctx, func(tx pgx.Tx) error {
 		var action string
 		var amount string
 		var currency string
@@ -479,7 +479,7 @@ func (s *Store) MarkBillingSettlementFailed(ctx context.Context, settlement Bill
 		taskStatus = "manual_review"
 		manualReason = "maximum settlement attempts exceeded"
 	}
-	return pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+	return s.beginTransaction(ctx, func(tx pgx.Tx) error {
 		tag, err := tx.Exec(ctx, `
 UPDATE settlement_outbox
 SET status = $3,