Add "Don't notify customer" option to Record Payment modal

Adds SuppressNotification to RecordPaymentDto and a checkbox to the
modal. When checked, the payment is fully recorded but NotifyPaymentReceivedAsync
is skipped — useful for historical imports or cases where the customer
should not receive an email.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -1335,14 +1335,17 @@ public class InvoicesController : Controller
 
             }); // end ExecuteInTransactionAsync
 
-            // Notify (non-blocking)
-            try
+            // Notify (non-blocking) — skipped if user explicitly suppressed it
+            if (!dto.SuppressNotification)
             {
-                await _notificationService.NotifyPaymentReceivedAsync(invoice, payment);
-            }
-            catch (Exception notifyEx)
-            {
-                _logger.LogWarning(notifyEx, "Payment recorded but notification failed");
+                try
+                {
+                    await _notificationService.NotifyPaymentReceivedAsync(invoice, payment);
+                }
+                catch (Exception notifyEx)
+                {
+                    _logger.LogWarning(notifyEx, "Payment recorded but notification failed");
+                }
             }