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/Services/IAuthService.cs

@@ -0,0 +1,18 @@
+using Meezi.API.Models.Auth;
+
+namespace Meezi.API.Services;
+
+public interface IAuthService
+{
+    Task<(bool Success, SendOtpResponse? Data, string? ErrorCode, string? ErrorMessage)> SendOtpAsync(
+        SendOtpRequest request,
+        CancellationToken cancellationToken = default);
+
+    Task<(bool Success, AuthTokenResponse? Data, string? ErrorCode, string? ErrorMessage)> VerifyOtpAsync(
+        VerifyOtpRequest request,
+        CancellationToken cancellationToken = default);
+
+    Task<(bool Success, AuthTokenResponse? Data, string? ErrorCode, string? ErrorMessage)> RefreshAsync(
+        RefreshTokenRequest request,
+        CancellationToken cancellationToken = default);
+}