feat: billing v2 — runtime-based plans, English UI, payment flow

- ServicePlan now has 'runtime' field (nodejs/laravel/wordpress)
- Admin billing page: Application Type dropdown, English UI, Toman prices
- calculateCost filters active plans by matching runtime
- Wallet page: English UI, payment gateway integration (Pay Now button)
- Deploy page Review step: billing cycle selector (hourly/monthly/yearly),
  payment method choice (wallet or payment gateway), Pay & Deploy button
- Payment gateway endpoints: POST /billing/gateway/initiate + /verify
  (simulated — ready for Zarinpal/IDPay integration)
- Deploy requires payment: wallet deduction or gateway charge before deploy

backend/src/billing/billing.controller.ts

@@ -112,6 +112,45 @@ export class BillingController {
     );
   }
 
+  // ─── Payment Gateway ─────────────────────────────────────────────
+
+  @Post('gateway/initiate')
+  @ApiOperation({ summary: 'Initiate a payment gateway transaction' })
+  async initiateGateway(
+    @Request() req: any,
+    @Body() body: { amount: number; description?: string; callbackUrl: string },
+  ) {
+    // In production, integrate with Zarinpal/IDPay/etc.
+    // For now, simulate a gateway redirect URL.
+    const trackingCode = `PAY-${Date.now()}-${Math.random().toString(36).substring(2, 8).toUpperCase()}`;
+    return {
+      success: true,
+      trackingCode,
+      gatewayUrl: `${body.callbackUrl}?trackingCode=${trackingCode}&amount=${body.amount}&status=success`,
+      message: 'Redirect user to gatewayUrl to complete payment',
+    };
+  }
+
+  @Post('gateway/verify')
+  @ApiOperation({ summary: 'Verify a payment gateway transaction and charge wallet' })
+  async verifyGateway(
+    @Request() req: any,
+    @Body() body: { trackingCode: string; amount: number },
+  ) {
+    // In production, verify with the gateway provider.
+    // For now, auto-approve and charge the wallet.
+    await this.billingService.chargeWallet(
+      req.user.id,
+      body.amount,
+      `Payment gateway: ${body.trackingCode}`,
+    );
+    return {
+      success: true,
+      message: 'Payment verified and wallet charged',
+      trackingCode: body.trackingCode,
+    };
+  }
+
   // ─── Wallet Admin ─────────────────────────────────────────────────
 
   @Get('admin/wallets')