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/Views/Invoices/Details.cshtml

@@ -1029,6 +1029,12 @@
                             <label class="form-label">Notes</label>
                             <textarea name="Notes" class="form-control" rows="2" placeholder="Optional"></textarea>
                         </div>
+                        <div class="form-check">
+                            <input class="form-check-input" type="checkbox" name="SuppressNotification" value="true" id="suppressNotificationCheck" />
+                            <label class="form-check-label text-muted small" for="suppressNotificationCheck">
+                                Don&rsquo;t notify customer
+                            </label>
+                        </div>
                     </div>
                     <div class="modal-footer">
                         <button type="button" class="btn btn-outline-secondary" data-bs-dismiss="modal">Cancel</button>