feat(billing): partner payout-ledger generation (worker + operator trigger)

Add BillingService.generatePayouts: idempotent per-partner/month/currency snapshot of gross MRR x marginPct into Payout rows (never rewrites a paid row), plus platformPayouts(). A PayoutWorker generates the current month daily (and on boot; PAYOUTS_AUTOGEN=false to disable). Operator endpoints GET /billing/payouts + POST /billing/payouts/generate, an operator payouts ledger table with a Generate button, and the proxy routes. The partner Payouts tab now shows real data.

services/platform-api/src/billing/billing.module.ts

@@ -12,6 +12,7 @@ import { UsersModule } from '../users/users.module.js'
 import { BillingService } from './billing.service.js'
 import { OperatorBillingController } from './operator-billing.controller.js'
 import { PartnerBillingController } from './partner-billing.controller.js'
+import { PayoutWorker } from './payout.worker.js'
 import { StripeWebhookController } from './stripe-webhook.controller.js'
 
 @Module({
@@ -29,6 +30,6 @@ import { StripeWebhookController } from './stripe-webhook.controller.js'
     UsersModule,
   ],
   controllers: [PartnerBillingController, OperatorBillingController, StripeWebhookController],
-  providers: [BillingService],
+  providers: [BillingService, PayoutWorker],
 })
 export class BillingModule {}