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/Index.razor.cs

@@ -17,6 +17,8 @@ public partial class Index : IDisposable
     [Inject] private GuestActionGate GuestGate { get; set; } = default!;
     [Inject] private VATService VAT { get; set; } = default!;
 
+    private bool _isAuthenticated;
+
     // ── CMS page data ──
     private PageSettingsDto? _pageData;
     private LandingSettings? _settings;
@@ -44,6 +46,7 @@ public partial class Index : IDisposable
     protected override async Task OnInitializedAsync()
     {
         MainService.OnChangeHandler += OnStateChanged;
+        _isAuthenticated = await AuthService.IsAuthenticatedAsync();
 
         // Load landing page settings from CMS
         try