fix(billing): compute plan expiry with Jalali months

Server/plugin/support charges used Gregorian Date#setMonth, so 3 months from 1405/06/01 became 1405/09/02. Now add N Jalali months minus one day (1405/08/30).

src/plugins/plugins.service.ts

@@ -11,6 +11,7 @@ import { PrismaService } from '../prisma/prisma.service';
 import { AuditService } from '../audit/audit.service';
 import { AdminNotifyService } from '../notifications/admin-notify.service';
 import {
+  addIranPlanExpiry,
   formatIranDate,
   iranDaysUntil,
   iranYmd,
@@ -204,7 +205,7 @@ export class PluginsService implements OnModuleInit, OnModuleDestroy {
       if (!PLUGIN_PLAN_MONTHS.includes(planMonths as any)) {
         throw new BadRequestException('مدت اشتراک نامعتبر است');
       }
-      expiresAt = this.addMonths(chargedAt, planMonths);
+      expiresAt = addIranPlanExpiry(chargedAt, planMonths);
     }
 
     const plugin = await this.prisma.pluginSubscription.create({
@@ -277,7 +278,7 @@ export class PluginsService implements OnModuleInit, OnModuleDestroy {
       chargedAt &&
       planMonths
     ) {
-      expiresAt = this.addMonths(chargedAt, planMonths);
+      expiresAt = addIranPlanExpiry(chargedAt, planMonths);
     }
 
     const plugin = await this.prisma.pluginSubscription.update({
@@ -329,7 +330,7 @@ export class PluginsService implements OnModuleInit, OnModuleDestroy {
     if (Number.isNaN(chargedAt.getTime())) {
       throw new BadRequestException('تاریخ شارژ نامعتبر است');
     }
-    const expiresAt = this.addMonths(chargedAt, dto.planMonths);
+    const expiresAt = addIranPlanExpiry(chargedAt, dto.planMonths);
 
     await this.prisma.$transaction([
       this.prisma.pluginSubscription.update({
@@ -541,14 +542,6 @@ export class PluginsService implements OnModuleInit, OnModuleDestroy {
     }
   }
 
-  private addMonths(from: Date, months: number) {
-    const d = new Date(from.getTime());
-    const day = d.getDate();
-    d.setMonth(d.getMonth() + months);
-    if (d.getDate() < day) d.setDate(0);
-    return d;
-  }
-
   private async requireTenant(tenantId: string) {
     const tenant = await this.prisma.tenant.findUnique({ where: { id: tenantId } });
     if (!tenant) throw new NotFoundException('نسخه یافت نشد');