fix: ManualPaymentDialog — remove hardcoded 56M, enable Amount field

- Default amount set to 0 (admin must enter)
- Amount field now editable with Required validation

src/BackOffice/Pages/Payment/Components/ManualPaymentDialog.razor

@@ -18,7 +18,9 @@
                                  Variant="Variant.Outlined"
                                  Adornment="Adornment.End"
                                  AdornmentText="تومان"
-                                 Disabled="true"
+                                 Required="true"
+                                 RequiredError="مبلغ الزامی است"
+                                 Min="1"
                                  @bind-Value="_createModel.Amount" />
 
                 <MudSelect T="int" 

src/BackOffice/Pages/Payment/Components/ManualPaymentDialog.razor.cs

@@ -30,7 +30,7 @@ public partial class ManualPaymentDialog
     [Parameter] public ManualPaymentModel? Model { get; set; }
 
     private ManualPaymentModel _createModel = new(){
-        Amount = 56000000,
+        Amount = 0,
     };
     private string? _adminNote;