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/SmsMarketingService.cs

@@ -0,0 +1,131 @@
+using Meezi.API.Models.Crm;
+using Meezi.Core.Constants;
+using Meezi.Core.Enums;
+using Meezi.Core.Interfaces;
+using Meezi.Core.Utilities;
+using Meezi.Infrastructure.Data;
+using Microsoft.EntityFrameworkCore;
+using StackExchange.Redis;
+
+namespace Meezi.API.Services;
+
+public interface ISmsMarketingService
+{
+    Task<SmsUsageDto> GetUsageAsync(string cafeId, PlanTier planTier, CancellationToken cancellationToken = default);
+    Task<(bool Success, SmsCampaignResult? Data, string? ErrorCode, string? Message)> SendCampaignAsync(
+        string cafeId,
+        PlanTier planTier,
+        SendSmsCampaignRequest request,
+        CancellationToken cancellationToken = default);
+}
+
+public class SmsMarketingService : ISmsMarketingService
+{
+    private readonly AppDbContext _db;
+    private readonly ISmsService _smsService;
+    private readonly IConnectionMultiplexer _redis;
+    private readonly ILogger<SmsMarketingService> _logger;
+
+    public SmsMarketingService(
+        AppDbContext db,
+        ISmsService smsService,
+        IConnectionMultiplexer redis,
+        ILogger<SmsMarketingService> logger)
+    {
+        _db = db;
+        _smsService = smsService;
+        _redis = redis;
+        _logger = logger;
+    }
+
+    public async Task<SmsUsageDto> GetUsageAsync(
+        string cafeId,
+        PlanTier planTier,
+        CancellationToken cancellationToken = default)
+    {
+        var month = DateTime.UtcNow.ToString("yyyy-MM");
+        var used = await GetUsedCountAsync(cafeId, month);
+        var limit = PlanLimits.MaxSmsPerMonth(planTier);
+        return new SmsUsageDto(used, limit == int.MaxValue ? -1 : limit, month);
+    }
+
+    public async Task<(bool Success, SmsCampaignResult? Data, string? ErrorCode, string? Message)> SendCampaignAsync(
+        string cafeId,
+        PlanTier planTier,
+        SendSmsCampaignRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        var maxSms = PlanLimits.MaxSmsPerMonth(planTier);
+        if (maxSms == 0)
+            return (false, null, "PLAN_LIMIT_REACHED", "SMS is not available on the Free plan.");
+
+        var phones = await ResolvePhonesAsync(cafeId, request, cancellationToken);
+        if (phones.Count == 0)
+            return (false, null, "NOT_FOUND", "No recipients found.");
+
+        var month = DateTime.UtcNow.ToString("yyyy-MM");
+        var used = await GetUsedCountAsync(cafeId, month);
+        if (maxSms != int.MaxValue && used + phones.Count > maxSms)
+            return (false, null, "PLAN_LIMIT_REACHED", "Monthly SMS limit would be exceeded.");
+
+        var sent = 0;
+        var failed = 0;
+
+        foreach (var phone in phones)
+        {
+            try
+            {
+                await _smsService.SendMessageAsync(phone, request.Message, cancellationToken);
+                sent++;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to send SMS to recipient");
+                failed++;
+            }
+        }
+
+        if (sent > 0)
+            await IncrementUsageAsync(cafeId, month, sent);
+
+        return (true, new SmsCampaignResult(sent, failed), null, null);
+    }
+
+    private async Task<List<string>> ResolvePhonesAsync(
+        string cafeId,
+        SendSmsCampaignRequest request,
+        CancellationToken cancellationToken)
+    {
+        if (request.Phones is { Count: > 0 })
+        {
+            return request.Phones
+                .Select(PhoneNormalizer.Normalize)
+                .Where(PhoneNormalizer.IsValidIranMobile)
+                .Distinct()
+                .ToList();
+        }
+
+        var query = _db.Customers.Where(c => c.CafeId == cafeId);
+        if (request.TargetGroup.HasValue)
+            query = query.Where(c => c.Group == request.TargetGroup.Value);
+
+        return await query.Select(c => c.Phone).Distinct().ToListAsync(cancellationToken);
+    }
+
+    private async Task<int> GetUsedCountAsync(string cafeId, string month)
+    {
+        var redis = _redis.GetDatabase();
+        var value = await redis.StringGetAsync(UsageKey(cafeId, month));
+        return value.HasValue ? (int)value : 0;
+    }
+
+    private async Task IncrementUsageAsync(string cafeId, string month, int count)
+    {
+        var redis = _redis.GetDatabase();
+        var key = UsageKey(cafeId, month);
+        await redis.StringIncrementAsync(key, count);
+        await redis.KeyExpireAsync(key, TimeSpan.FromDays(40));
+    }
+
+    private static string UsageKey(string cafeId, string month) => $"sms:usage:{cafeId}:{month}";
+}