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/Club/MembershipPage.razor

@@ -70,7 +70,7 @@
                         <MudIcon Icon="@Icons.Material.Filled.AccountBalanceWallet" Color="Color.Success" Size="Size.Large" />
                         <MudStack Spacing="0">
                             <MudText Typo="Typo.subtitle1">شارژ کیف پول فروشگاه اعتباری</MudText>
-                            <MudText Typo="Typo.caption" Color="Color.Default">شارژ ۵۶ میلیون تومان کیف پول فروشگاه اعتباری</MudText>
+                            <MudText Typo="Typo.caption" Color="Color.Default">شارژ برابر ارزش پکیج فعال در کیف پول فروشگاه اعتباری</MudText>
                         </MudStack>
                     </MudStack>
                     <MudDivider />