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/Pages/DiscountStore/Cart.razor.cs

@@ -7,9 +7,15 @@ public partial class Cart : IDisposable
 {
     [Inject] private DiscountCartService DiscountCart { get; set; } = default!;
     [Inject] private VATService VAT { get; set; } = default!;
+    [Inject] private AuthDialogService AuthDialogService { get; set; } = default!;
+    [Inject] private AuthService AuthService { get; set; } = default!;
 
     protected override async Task OnInitializedAsync()
     {
+        if (!await AuthService.IsAuthenticatedAsync())
+        {
+            await AuthDialogService.ShowAuthDialogAsync();
+        }
         await DiscountCart.EnsureInitializedAsync();
         DiscountCart.OnChange += StateHasChanged;
     }

src/FrontOffice.Main/Pages/DiscountStore/Checkout.razor.cs

@@ -11,6 +11,8 @@ public partial class Checkout
     [Inject] private DiscountOrderService DiscountOrderService { get; set; } = default!;
     [Inject] private UserAddressContract.UserAddressContractClient UserAddressContract { get; set; } = default!;
     [Inject] private VATService VAT { get; set; } = default!;
+    [Inject] private AuthDialogService AuthDialogService { get; set; } = default!;
+    [Inject] private AuthService AuthService { get; set; } = default!;
 
     private List<CustomerAddressModel> _addresses = new();
     private CustomerAddressModel? _selectedAddress;
@@ -32,6 +34,10 @@ public partial class Checkout
 
     protected override async Task OnInitializedAsync()
     {
+        if (!await AuthService.IsAuthenticatedAsync())
+        {
+            await AuthDialogService.ShowAuthDialogAsync();
+        }
         await VAT.LoadAsync();
         await DiscountCart.EnsureInitializedAsync();
         await LoadAddresses();

src/FrontOffice.Main/Pages/DiscountStore/ProductDetail.razor.cs

@@ -10,6 +10,7 @@ public partial class ProductDetail
     [Inject] private DiscountProductService DiscountProductService { get; set; } = default!;
     [Inject] private DiscountCartService DiscountCartService { get; set; } = default!;
     [Inject] private VATService VAT { get; set; } = default!;
+    [Inject] private GuestActionGate GuestGate { get; set; } = default!;
 
     private DiscountProductDetail? _product;
     private string _selectedImage = string.Empty;
@@ -59,8 +60,14 @@ public partial class ProductDetail
         _addingToCart = true;
         try
         {
-            await DiscountCartService.AddAsync(_product.Id, _quantity);
-            Snackbar.Add($"{_product.Title} به سبد خرید اضافه شد", MudBlazor.Severity.Success);
+            var productId = _product.Id;
+            var qty = _quantity;
+            var title = _product.Title;
+            await GuestGate.RunAsync(async () =>
+            {
+                await DiscountCartService.AddAsync(productId, qty);
+                Snackbar.Add($"{title} به سبد خرید اضافه شد", MudBlazor.Severity.Success);
+            });
         }
         catch
         {

src/FrontOffice.Main/Pages/DiscountStore/Products.razor.cs

@@ -8,6 +8,7 @@ public partial class Products : ComponentBase, IDisposable
 {
     [Inject] private DiscountProductService ProductService { get; set; } = default!;
     [Inject] private DiscountCartService DiscountCart { get; set; } = default!;
+    [Inject] private GuestActionGate GuestGate { get; set; } = default!;
 
     private string _search = string.Empty;
     private long? _selectedCategoryId;
@@ -94,7 +95,7 @@ public partial class Products : ComponentBase, IDisposable
 
     private async Task AddToCart(DiscountProductCard p)
     {
-        await DiscountCart.AddAsync(p.Id);
+        await GuestGate.RunAsync(() => DiscountCart.AddAsync(p.Id));
     }
 
     private void NavigateToProduct(long id)