refactor: remove PaymentChannel, reuse upstream Channel with features field

- Delete payment_channels table and PaymentChannel Ent schema
- Add `features` column to upstream channels table (migration 095)
- Add Features field to Channel struct, input types, handler request/response
- Payment user/admin handlers now use ChannelService directly
- Remove Channel CRUD from PaymentConfigService and admin payment routes
- Remove "渠道管理" tab from admin orders page (use /admin/channels)

backend/ent/intercept/intercept.go

@@ -336,6 +336,7 @@ func (f TraversePaymentAuditLog) Traverse(ctx context.Context, q ent.Query) erro
 	return fmt.Errorf("unexpected query type %T. expect *ent.PaymentAuditLogQuery", q)
 }
 
+
 // The PaymentOrderFunc type is an adapter to allow the use of ordinary function as a Querier.
 type PaymentOrderFunc func(context.Context, *ent.PaymentOrderQuery) (ent.Value, error)