Add invoice payment management.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/billing/dto/billing.dto.ts

@@ -1,7 +1,7 @@
 import { IsString, IsEnum, IsOptional, IsBoolean, IsNumber, IsArray, ValidateNested, Min } from 'class-validator';
 import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
 import { Type } from 'class-transformer';
-import { BillingCycle, PricingResourceType, AppRuntime } from '../../common/enums';
+import { BillingCycle, PricingResourceType, AppRuntime, InvoiceStatus } from '../../common/enums';
 import { OptionalServiceResourcesDto } from './optional-service-resources.dto';
 
 export class CreatePricingRuleDto {
@@ -210,6 +210,35 @@ export class UpgradeResourcesDto {
 
 export class CalculateUpgradeCostDto extends UpgradeResourcesDto {}
 
+// ─── Invoice DTOs ───────────────────────────────────────────────────
+
+export class InitiateInvoicePaymentDto {
+  @ApiProperty({ example: 'https://app.example.com/dashboard/invoices' })
+  @IsString()
+  callbackUrl: string;
+}
+
+export class VerifyInvoiceGatewayDto {
+  @ApiProperty({ example: 'INV-1710000000000-ABC123' })
+  @IsString()
+  trackingCode: string;
+
+  @ApiProperty({ example: 50000 })
+  @IsNumber()
+  @Min(1)
+  amount: number;
+}
+
+export class UpdateInvoiceStatusDto {
+  @ApiProperty({ enum: InvoiceStatus })
+  @IsEnum(InvoiceStatus)
+  status: InvoiceStatus;
+
+  @ApiProperty({ example: 'Manual reconciliation by finance team' })
+  @IsString()
+  reason: string;
+}
+
 // ─── Platform optional services pricing (Admin) ─────────────────────
 
 export class OptionalServiceCyclePricesDto {