feat: implement VAT management service and integrate VAT calculations across components

src/FrontOffice.Main/Pages/Store/Cart.razor.cs

@@ -7,12 +7,16 @@ namespace FrontOffice.Main.Pages.Store;
 public partial class Cart : ComponentBase, IDisposable
 {
     [Inject] private CartService CartService { get; set; } = default!;
+    [Inject] private VATService VAT { get; set; } = default!;
     // Navigation and Snackbar are available via _Imports.razor
     private CartService CartData => CartService;
 
-    protected override void OnInitialized()
+    protected override async Task OnInitializedAsync()
     {
+        // لود سبد خرید (فقط اگر کاربر لاگین کرده باشد)
+        await CartService.EnsureInitializedAsync();
         CartService.OnChange += StateHasChanged;
+        await VAT.LoadAsync();
     }
 
     private async Task IncrementQty(long productId)
@@ -44,7 +48,13 @@ public partial class Cart : ComponentBase, IDisposable
         Navigation.NavigateTo(RouteConstants.Store.CheckoutSummary);
     }
 
-    private static string FormatPrice(long price) => string.Format("{0:N0} ", price);
+    private string FormatPrice(long price) => $"{price:N0} ";
+    
+    private string FormatPriceWithVAT(long price) => $"{VAT.AddVAT(price):N0} ";
+    
+    private long TotalWithVAT => VAT.AddVAT(CartData.Total);
+    
+    private long VATAmount => VAT.CalculateVAT(CartData.Total);
 
     private static string GetProductImageUrl(string? imageUrl)
         => string.IsNullOrWhiteSpace(imageUrl) ? "/images/product-placeholder.svg" : imageUrl;