fix: onboarding 401 redirect, glass card rendering bugs

- rpc-client: don't redirect to /login on 401 during onboarding flow,
  which caused session expired kicks on fresh installs
- style.css: add translateZ(0) + isolation:isolate to glass-card,
  glass-strong, path-option-card to fix Chromium compositor bug where
  backdrop-filter + animated fixed overlays cause black rectangles
- App.vue: pause background animations when tab hidden, force
  compositor layer rebuild on tab return to prevent stale renders

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/App.vue

@@ -168,7 +168,28 @@ const isReady = ref(false)
  * - User has already seen the intro
  * - User is on a direct route (refresh/bookmark)
  */
+// Fix Chromium backdrop-filter rendering bug: when tab loses/regains focus,
+// the compositor fails to repaint backdrop-filter layers over animated
+// fixed-position overlays (body::before/after with mix-blend-mode).
+// On return: strip backdrop-filter via class, wait a frame, then restore.
+function onVisibilityChange() {
+  if (document.hidden) {
+    document.documentElement.classList.add('tab-hidden')
+  } else {
+    // Step 1: kill all backdrop-filters (forces compositor to drop those layers)
+    document.documentElement.classList.add('no-backdrop')
+    document.documentElement.classList.remove('tab-hidden')
+    // Step 2: next frame, re-enable (compositor builds fresh layers)
+    requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        document.documentElement.classList.remove('no-backdrop')
+      })
+    })
+  }
+}
+
 onMounted(async () => {
+  document.addEventListener('visibilitychange', onVisibilityChange)
   window.addEventListener('keydown', onKeyDown, true)
   window.addEventListener('mousemove', onUserActivity)
   window.addEventListener('mousedown', onUserActivity)
@@ -196,6 +217,7 @@ onMounted(async () => {
 })
 
 onBeforeUnmount(() => {
+  document.removeEventListener('visibilitychange', onVisibilityChange)
   window.removeEventListener('keydown', onKeyDown, true)
   window.removeEventListener('mousemove', onUserActivity)
   window.removeEventListener('mousedown', onUserActivity)