feat: hide product prices from unauthenticated (guest) users

Guests can browse products and product details for presentation purposes,
but prices are hidden behind a 'وارد شوید' prompt (lock icon).
Authenticated users see prices as before.

Affected pages:
- Landing page (Index): top-selling regular + discount sections
- Store/Products list
- Store/ProductDetail (desktop price + mobile sticky bar)
- DiscountStore/Products list
- DiscountStore/ProductDetail (full price box)

Each code-behind now checks AuthService.IsAuthenticatedAsync() on init
and stores the result in _isAuthenticated for use in the template.

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

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

@@ -11,6 +11,9 @@ public partial class ProductDetail
     [Inject] private DiscountCartService DiscountCartService { get; set; } = default!;
     [Inject] private VATService VAT { get; set; } = default!;
     [Inject] private GuestActionGate GuestGate { get; set; } = default!;
+    [Inject] private AuthService AuthService { get; set; } = default!;
+
+    private bool _isAuthenticated;
 
     private DiscountProductDetail? _product;
     private string _selectedImage = string.Empty;
@@ -20,6 +23,7 @@ public partial class ProductDetail
 
     protected override async Task OnInitializedAsync()
     {
+        _isAuthenticated = await AuthService.IsAuthenticatedAsync();
         await LoadProductAsync();
     }