feat: add top-seller product sections to landing page with guest browsing support

- Add two sections to landing page (Index.razor) below the hero:
  - Top 6 best-selling regular products (3-per-row grid)
  - Top 6 best-selling discount store products (3-per-row grid)
  - Each section has a 'More' button linking to /products and /discount-store
- Add GuestActionGate utility service: wraps auth-required actions; shows
  login modal for guests and resumes the original action after successful login
- Register GuestActionGate as scoped service in ConfigureServices
- Add GetTopSellingAsync(count) to ProductService and DiscountProductService
- Add optional sortBy parameter to DiscountProductService.GetProductsAsync
- Hybridize all product pages for guest browsing:
  - Store/Products, Store/ProductDetail: wrap AddToCart with GuestActionGate
  - DiscountStore/Products, DiscountStore/ProductDetail: wrap AddToCart with GuestActionGate
  - Store/Cart, DiscountStore/Cart, Store/CheckoutSummary: soft auth gate on page init
- Fix MembershipPage membership benefit text to be package-agnostic

Co-authored-by: Cursor <cursoragent@cursor.com>

src/FrontOffice.Main/Utilities/DiscountProductService.cs

@@ -80,7 +80,7 @@ public class DiscountProductService
     public async Task<DiscountProductListResult> GetProductsAsync(
         int page = 1, int pageSize = 12,
         string? search = null, long? categoryId = null,
-        bool? inStock = null)
+        bool? inStock = null, string? sortBy = null)
     {
         try
         {
@@ -97,6 +97,8 @@ public class DiscountProductService
                 request.CategoryId = categoryId.Value;
             if (inStock.HasValue)
                 request.InStock = inStock.Value;
+            if (!string.IsNullOrWhiteSpace(sortBy))
+                request.SortBy = sortBy;
 
             var response = await _productClient.GetDiscountProductsAsync(request);
 
@@ -125,6 +127,9 @@ public class DiscountProductService
         }
     }
 
+    public Task<DiscountProductListResult> GetTopSellingAsync(int count = 6)
+        => GetProductsAsync(page: 1, pageSize: count, sortBy: "SaleCount desc");
+
     public async Task<DiscountProductDetail?> GetByIdAsync(long productId)
     {
         try

src/FrontOffice.Main/Utilities/GuestActionGate.cs

@@ -0,0 +1,42 @@
+namespace FrontOffice.Main.Utilities;
+
+/// <summary>
+/// هر action ای که نیاز به لاگین دارد را از طریق این سرویس اجرا کنید.
+/// اگر کاربر لاگین نباشد، مودال ورود نشان داده می‌شود.
+/// پس از ورود موفق، action به صورت خودکار اجرا می‌شود.
+/// </summary>
+public class GuestActionGate
+{
+    private readonly AuthService _authService;
+    private readonly AuthDialogService _authDialogService;
+
+    public GuestActionGate(AuthService authService, AuthDialogService authDialogService)
+    {
+        _authService = authService;
+        _authDialogService = authDialogService;
+    }
+
+    /// <summary>
+    /// اگر کاربر لاگین باشد action را اجرا می‌کند.
+    /// در غیر این صورت مودال لاگین را باز کرده و پس از ورود موفق، action را اجرا می‌کند.
+    /// </summary>
+    /// <returns>true اگر action اجرا شد، false اگر کاربر لاگین نکرد.</returns>
+    public async Task<bool> RunAsync(Func<Task> action)
+    {
+        if (await _authService.IsAuthenticatedAsync())
+        {
+            await action();
+            return true;
+        }
+
+        await _authDialogService.ShowAuthDialogAsync();
+
+        if (await _authService.IsAuthenticatedAsync())
+        {
+            await action();
+            return true;
+        }
+
+        return false;
+    }
+}

src/FrontOffice.Main/Utilities/ProductService.cs

@@ -71,6 +71,9 @@ public class ProductService
         return result.Products;
     }
 
+    public Task<ProductListResult> GetTopSellingAsync(int count = 6)
+        => GetProductsPagedAsync(sortBy: "SaleCount desc", page: 1, pageSize: count);
+
     public async Task<ProductListResult> GetProductsPagedAsync(
         string? query = null, long? categoryId = null, string? sortBy = null,
         int page = 1, int pageSize = 12)