fix(dashboard): Disable DiscountShopWidget temporarily

- Comment out DiscountShopWidget that requires unregistered IDiscountOrderService
- Add placeholder card with 'coming soon' message
- Fix null reference warnings with null! attributes

src/BackOffice/Pages/Dashboard/SystemOverview.razor

@@ -139,8 +139,24 @@
             </MudCardContent>
         </MudCard>
 
-        <!-- Discount Shop Stats -->
+        <!-- Discount Shop Stats - TEMPORARILY DISABLED (needs DiscountOrder proto) -->
-        <BackOffice.Pages.Dashboard.DiscountShopWidget />
+        @* <BackOffice.Pages.Dashboard.DiscountShopWidget /> *@
+        
+        <MudCard Class="mb-4">
+            <MudCardHeader>
+                <CardHeaderContent>
+                    <MudText Typo="Typo.h6">
+                        <MudIcon Icon="@Icons.Material.Filled.Discount" Class="mr-2" />
+                        آمار فروشگاه تخفیفی
+                    </MudText>
+                </CardHeaderContent>
+            </MudCardHeader>
+            <MudCardContent>
+                <MudAlert Severity="Severity.Info" Dense="true">
+                    این بخش در حال توسعه است و به‌زودی فعال می‌شود.
+                </MudAlert>
+            </MudCardContent>
+        </MudCard>
 
         <!-- Quick Actions -->
         <MudCard>
@@ -215,8 +231,8 @@
 </MudContainer>
 
 @code {
-    [Inject] public CommissionContract.CommissionContractClient CommissionClient { get; set; }
+    [Inject] public CommissionContract.CommissionContractClient CommissionClient { get; set; } = null!;
-    [Inject] public ClubMembershipContract.ClubMembershipContractClient ClubClient { get; set; }
+    [Inject] public ClubMembershipContract.ClubMembershipContractClient ClubClient { get; set; } = null!;
 
     private bool _loading = false;
     private long _currentWeekDefinitionId = 0;