fix: mobile onboarding viewport + filebrowser demo fixes

Onboarding:
- Fixed viewport to use dvh units with position:fixed container
- All views use scrollable glass containers that fit within viewport
- Responsive typography and spacing (mobile-first breakpoints)
- Tighter padding/margins on small screens
- RootRedirect checks localStorage first for instant redirect
- Spinner only appears after 500ms delay to avoid flash

Filebrowser:
- Fix CloudFolder null initialPath crash (watch both useNativeUI + section)
- Remove unused `host` computed (was causing TS error)
- Add mock GET /app/filebrowser/ landing page
- Increase express.json limit to 50mb

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

neode-ui/src/views/RootRedirect.vue

@@ -1,11 +1,10 @@
 <template>
-  <div class="min-h-screen flex items-center justify-center bg-black/40">
-    <div class="flex flex-col items-center gap-4">
-      <svg class="animate-spin h-10 w-10 text-white/80" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24">
+  <div class="min-h-full flex items-center justify-center">
+    <div class="flex flex-col items-center gap-4 opacity-0 root-redirect-fade">
+      <svg class="animate-spin h-8 w-8 text-white/60" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24">
         <circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"></circle>
         <path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path>
       </svg>
-      <p class="text-white/60 text-sm">Loading...</p>
     </div>
   </div>
 </template>
@@ -24,16 +23,33 @@ onMounted(async () => {
     return
   }
 
+  // Check localStorage first for instant redirect (avoids 5s timeout)
+  const localComplete = localStorage.getItem('neode_onboarding_complete') === '1'
+  if (localComplete) {
+    router.replace('/login').catch(() => {})
+    return
+  }
+
   let seenOnboarding = false
   try {
     const result = await Promise.race([
       isOnboardingComplete(),
-      new Promise<boolean>((resolve) => setTimeout(() => resolve(false), 5000)),
+      new Promise<boolean>((resolve) => setTimeout(() => resolve(false), 3000)),
     ])
     seenOnboarding = result
   } catch {
-    seenOnboarding = localStorage.getItem('neode_onboarding_complete') === '1'
+    seenOnboarding = false
   }
   router.replace(seenOnboarding ? '/login' : '/onboarding/intro').catch(() => {})
 })
 </script>
+
+<style scoped>
+/* Only show spinner after 500ms delay — most redirects happen instantly */
+.root-redirect-fade {
+  animation: root-fade-in 0.3s ease 0.5s forwards;
+}
+@keyframes root-fade-in {
+  to { opacity: 1; }
+}
+</style>