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/Hubs/.gitkeep

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+

src/Meezi.API/Hubs/GuestOrderHub.cs

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+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+using Meezi.Infrastructure.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Meezi.API.Hubs;
+
+[AllowAnonymous]
+public class GuestOrderHub : Hub
+{
+    public static string OrderGroup(string orderId) => $"guest-order:{orderId}";
+
+    public async Task JoinOrder(string orderId, string trackingToken)
+    {
+        if (string.IsNullOrWhiteSpace(orderId) || string.IsNullOrWhiteSpace(trackingToken))
+            throw new HubException("Invalid order.");
+
+        var db = Context.GetHttpContext()?.RequestServices.GetRequiredService<AppDbContext>();
+        if (db is null)
+            throw new HubException("Unavailable.");
+
+        var valid = await db.Orders.AsNoTracking()
+            .AnyAsync(o => o.Id == orderId && o.GuestTrackingToken == trackingToken);
+
+        if (!valid)
+            throw new HubException("Forbidden.");
+
+        await Groups.AddToGroupAsync(Context.ConnectionId, OrderGroup(orderId));
+    }
+
+    public Task LeaveOrder(string orderId) =>
+        Groups.RemoveFromGroupAsync(Context.ConnectionId, OrderGroup(orderId));
+}

src/Meezi.API/Hubs/KdsHub.cs

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+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+using Meezi.Core.Constants;
+
+namespace Meezi.API.Hubs;
+
+[Authorize]
+public class KdsHub : Hub
+{
+    public static string GroupName(string cafeId) => $"cafe:{cafeId}";
+
+    public async Task JoinCafe(string cafeId)
+    {
+        var claimCafeId = Context.User?.FindFirst(MeeziClaimTypes.CafeId)?.Value;
+        if (string.IsNullOrEmpty(claimCafeId) || claimCafeId != cafeId)
+            throw new HubException("Forbidden");
+
+        await Groups.AddToGroupAsync(Context.ConnectionId, GroupName(cafeId));
+    }
+
+    public Task LeaveCafe(string cafeId) =>
+        Groups.RemoveFromGroupAsync(Context.ConnectionId, GroupName(cafeId));
+}