feat(api): .NET 10 multi-tenant REST API

Full backend implementation:
- Multi-tenant cafe/restaurant management (menus, orders, tables, staff)
- POS order flow with ZarinPal and Snappfood payment integration
- OTP authentication via Kavenegar SMS
- QR digital menu with public discover/finder endpoints
- Customer loyalty, coupons, CRM
- PostgreSQL via EF Core, Redis for caching/sessions
- Background jobs, webhook handlers
- Full migration history

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/Meezi.API/Models/Billing/BillingDtos.cs

@@ -0,0 +1,27 @@
+using Meezi.Core.Enums;
+
+namespace Meezi.API.Models.Billing;
+
+public record SubscribeRequest(PlanTier PlanTier, int Months, string? PaymentMethod = null);
+
+public record PaymentMethodDto(string Id, string DisplayNameFa, bool IsDefault);
+
+public record SubscribeResponse(string PaymentId, string PaymentUrl);
+
+public record BillingStatusDto(
+    PlanTier PlanTier,
+    DateTime? PlanExpiresAt,
+    int OrdersToday,
+    int? OrdersDailyLimit,
+    int CustomersCount,
+    int? CustomersLimit,
+    int SmsUsedThisMonth,
+    int SmsMonthlyLimit,
+    bool Menu3dEnabled,
+    bool MenuAi3dEnabled,
+    int MenuAi3dUsedThisMonth,
+    int MenuAi3dMonthlyLimit,
+    bool DiscoverProfileEnabled,
+    bool IsPlanExpired);
+
+public record BillingVerifyResult(bool Success, string RedirectUrl);