Fix notification bell, SMS consent kiosk flow, and button alignment

Notification bell:
- Bell now polls /InAppNotifications/Recent every 60s as a SignalR fallback
- Bell dropdown refresh on open so count is always current when staff looks at it

SMS consent → kiosk flow:
- Staff clicks "Get SMS Consent" on Customer Details → AJAX POST to
  /Kiosk/PushSmsConsent stores customer in IMemoryCache (10 min TTL)
- Kiosk PollSession returns smsConsentPending + customerId so tablet navigates
  to /Kiosk/SmsConsent/{customerId} automatically
- Customer reads TCPA consent on tablet, taps I Agree or No Thanks
- On agree: NotifyBySms/SmsConsentedAt/SmsConsentMethod set; in-app notification
  fires; cache cleared; tablet returns to Welcome
- Removed Customers/SmsConsent (staff-browser version); moved view to Kiosk/

Button alignment:
- kiosk.css: added display:flex + align-items:center + justify-content:center to
  all kiosk body buttons so content is centred vertically in tall button outlines

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

src/PowderCoating.Web/wwwroot/css/kiosk.css

@@ -60,6 +60,14 @@ body.kiosk-body {
     width: 100%;
 }
 
+/* Vertically centre content in any tall kiosk button (covers <a> and <button>) */
+.kiosk-body .btn,
+.kiosk-btn {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+}
+
 /* Suppress all hover effects on touch screens */
 @media (hover: none) {
     .kiosk-body .btn:hover { filter: none; opacity: 1; }