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

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

@@ -10,6 +10,7 @@ public partial class CheckoutSummary : ComponentBase
 {
     [Inject] private CartService Cart { get; set; } = default!;
     [Inject] private OrderService OrderService { get; set; } = default!;
+    [Inject] private VATService VAT { get; set; } = default!;
     [Inject] private UserAddressContract.UserAddressContractClient UserAddressContract { get; set; } = default!;
     [Inject] private UserOrderContract.UserOrderContractClient UserOrderContract { get; set; } = default!;
     // Snackbar and Navigation are injected via _Imports.razor
@@ -25,8 +26,11 @@ public partial class CheckoutSummary : ComponentBase
 
     protected override async Task OnInitializedAsync()
     {
+        // لود سبد خرید (فقط اگر کاربر لاگین کرده باشد)
+        await Cart.EnsureInitializedAsync();
         await LoadAddresses();
         await LoadWalletBalance();
+        await VAT.LoadAsync();
     }
 
     private async Task LoadWalletBalance()
@@ -92,9 +96,9 @@ public partial class CheckoutSummary : ComponentBase
     private static string FormatPrice(long price) => string.Format("{0:N0} تومان", price);
 
     /// <summary>
-    /// محاسبه مالیات بر ارزش افزوده (۹%)
+    /// محاسبه مالیات بر ارزش افزوده
     /// </summary>
-    private long CalculateVAT() => (long)(Cart.Total * 0.09);
+    private long CalculateVAT() => VAT.CalculateVAT(Cart.Total);
 
     private static string GetProductImageUrl(string? imageUrl)
         => string.IsNullOrWhiteSpace(imageUrl) ? "/images/product-placeholder.svg" : imageUrl;