fix(kiosk): no reload on first service-worker claim + patient boot health check

Two causes of the fresh-install 'loads, refreshes, loads again' jank:

- The PWA autoUpdate service worker claims the page right after the very
  first load, firing controllerchange, which unconditionally reloaded the
  page. Now only a *replaced* controller (a real update) triggers reload.
- A single 2s RPC echo decided server-down on first boot, flashing the
  BootScreen and then hard-reloading seconds later. A second, 6s attempt
  now runs before concluding the backend is down.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/components/PWAUpdatePrompt.vue

@@ -32,8 +32,18 @@ let updateCallback: (() => Promise<void>) | null = null
 onMounted(() => {
   // Listen for service worker updates
   if ('serviceWorker' in navigator) {
+    // On the very first visit the page loads with no controlling SW; the
+    // freshly-installed worker then activates and claims the page
+    // (autoUpdate → clientsClaim), firing controllerchange. Reloading on
+    // that first claim caused the fresh-install "loads, then reloads"
+    // jank (worst on kiosk). Only reload when an existing controller is
+    // REPLACED — i.e. a genuine update.
+    let hadController = !!navigator.serviceWorker.controller
     navigator.serviceWorker.addEventListener('controllerchange', () => {
-      // Service worker updated, reload the page
+      if (!hadController) {
+        hadController = true
+        return
+      }
       window.location.reload()
     })