feat: ChargeDiscountWallet UI - page, route, client method & wallet link

- Add ChargeDiscountWallet.razor page with charge form and preset amounts
- Add ChargeDiscountWallet.razor.cs code-behind with gateway redirect logic
- Add InitiateDiscountChargeAsync client method in WalletService
- Add ChargeDiscountWallet route constant
- Add charge button link on main Wallet page

src/FrontOffice.Main/Pages/Profile/Wallet.razor

@@ -38,6 +38,17 @@
             درخواست‌های برداشت
         </MudButton>
 
+        <!-- دکمه شارژ کیف‌پول اعتباری -->
+        <MudButton Variant="Variant.Filled" 
+                   Color="Color.Info" 
+                   Size="Size.Large"
+                   FullWidth="true"
+                   StartIcon="@Icons.Material.Filled.CreditCard"
+                   Href="@RouteConstants.Profile.ChargeDiscountWallet"
+                   Class="rounded-lg">
+            شارژ کیف‌پول اعتباری
+        </MudButton>
+
         <MudPaper Elevation="2" Class="pa-4 rounded-lg">
             <MudText Typo="Typo.h6" Class="mb-2">تراکنش‌ها و مسیرهای شارژ</MudText>