feat(lifecycle): add billing lifecycle with auto-suspend/delete

- New AppLifecycleService with cron-based scanner (60s interval)
- State machine: ACTIVE → SUSPENDED → PENDING_DELETION → DELETED
- Auto-renew hourly plans from wallet
- Admin-configurable grace periods via PlatformSettings table
- New LifecycleController (GET/PATCH /lifecycle/settings)
- PlatformSetting entity for runtime admin config
- BillingService: calculateCostForApp, deductWallet
- Application entity: planId, billingCycle, lifecycleStatus, planExpiresAt
- New enums: AppLifecycleStatus, BillingCycle

backend/src/billing/billing.service.ts

@@ -288,4 +288,27 @@ export class BillingService {
   async getAllWallets(): Promise<Wallet[]> {
     return this.walletRepo.find({ relations: ['user'], order: { balance: 'DESC' } });
   }
+
+  /**
+   * Calculate cost for an existing Application entity.
+   * Used by lifecycle service for auto-renew.
+   */
+  async calculateCostForApp(app: {
+    runtime: string;
+    databaseType: string;
+    cpuLimit: string;
+    memoryLimit: string;
+    replicas: number;
+    dbStorageSize?: string;
+  }): Promise<{ hourly: number; monthly: number; yearly: number }> {
+    const result = await this.calculateCost({
+      runtime: app.runtime,
+      databaseType: app.databaseType,
+      cpuLimit: app.cpuLimit,
+      memoryLimit: app.memoryLimit,
+      replicas: app.replicas,
+      dbStorageSize: app.dbStorageSize,
+    });
+    return { hourly: result.hourly, monthly: result.monthly, yearly: result.yearly };
+  }
 }