Fix: Import concurrency errors + Add sales data cleanup

- Fix optimistic concurrency errors in product import by using ExecuteSqlRaw instead of EF tracking
- Add DeleteAllOrdersAndSalesDataAsync() method to clear orders, payments, customers, and messages
- Add DeleteAllSalesData endpoint to ProductsController for admin access
- Proper deletion order to avoid foreign key violations
- Enhanced logging for troubleshooting data cleanup operations

Resolves: Import errors with 'database operation expected to affect 1 row(s)'

LittleShop/Areas/Admin/Controllers/ProductsController.cs

@@ -306,4 +306,21 @@ public class ProductsController : Controller
         }
         return Json(collection);
     }
+
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    public async Task<IActionResult> DeleteAllSalesData()
+    {
+        try
+        {
+            var deletedCount = await _importService.DeleteAllOrdersAndSalesDataAsync();
+            TempData["SuccessMessage"] = $"✅ Successfully deleted {deletedCount} sales records (orders, payments, customers, messages)";
+            return RedirectToAction(nameof(Index));
+        }
+        catch (Exception ex)
+        {
+            TempData["ErrorMessage"] = $"Failed to delete sales data: {ex.Message}";
+            return RedirectToAction(nameof(Index));
+        }
+    }
 }