Fix kiosk SMS consent routing loop and stuck tablet

- Route param renamed customerId→id so /Kiosk/SmsConsent/15307 binds correctly
  (default MVC route uses {id}; mismatched name caused GetByIdAsync(0)→404→loop)
- Cache entry cleared in GET (not just POST) so returning to Welcome after seeing
  the form never redirects again
- Added POST /Kiosk/CancelSmsConsent for staff to free the kiosk if they pushed
  consent accidentally — Customer Details shows a Cancel button after pushing

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

src/PowderCoating.Web/wwwroot/js/customer-details.js

@@ -10,6 +10,8 @@ async function pushSmsConsent(customerId) {
         const data = await res.json();
         if (data.success) {
             toastr.success('Consent form sent to the kiosk tablet — hand it to the customer.', 'Sent to Kiosk');
+            document.getElementById('btnGetSmsConsent')?.classList.add('d-none');
+            document.getElementById('btnCancelSmsConsent')?.classList.remove('d-none');
         } else {
             toastr.warning(data.message || 'Could not send consent to kiosk.');
         }
@@ -17,3 +19,21 @@ async function pushSmsConsent(customerId) {
         toastr.error('An error occurred. Please try again.');
     }
 }
+
+async function cancelSmsConsent() {
+    const tok = document.querySelector('input[name="__RequestVerificationToken"]')?.value ?? '';
+    try {
+        const res  = await fetch('/Kiosk/CancelSmsConsent', {
+            method:  'POST',
+            headers: { 'RequestVerificationToken': tok }
+        });
+        const data = await res.json();
+        if (data.success) {
+            toastr.info('Consent request cancelled — kiosk is free.');
+            document.getElementById('btnCancelSmsConsent')?.classList.add('d-none');
+            document.getElementById('btnGetSmsConsent')?.classList.remove('d-none');
+        }
+    } catch {
+        toastr.error('An error occurred. Please try again.');
+    }
+}