Replace kiosk SignalR with polling — Azure App Service blocks anonymous hub handshakes

SignalR WebSocket and SSE both receive immediate 'Handshake was canceled' from the
server-side hub context. The 15-second delay between negotiate and SSE connect
reveals the handshake timer has expired before the transport opens — caused by Azure
App Service's ingress proxy resetting anonymous long-lived connections.

Replacement: /Kiosk/PollSession (anonymous GET, no-cache) queried every 3 seconds.
Returns the most recent Active InPerson session created in the last 60 seconds.
The kiosk navigates when hasSession=true. Status dot: gray->green on first success,
yellow on network error, blue when navigating. Removed signalr.min.js from kiosk layout.

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

src/PowderCoating.Web/Views/Shared/_KioskLayout.cshtml

@@ -85,7 +85,6 @@
 }
 
 <script src="~/lib/bootstrap/js/bootstrap.bundle.min.js"></script>
-<script src="~/lib/microsoft/signalr/dist/browser/signalr.min.js"></script>
 @await RenderSectionAsync("Scripts", required: false)
 </body>
 </html>