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/OnboardingDid.vue

@@ -1,13 +1,13 @@
 <template>
-  <div class="min-h-screen flex items-center justify-center p-4">
+  <div class="min-h-full flex items-center justify-center p-3 sm:p-4 md:p-6">
     <!-- Main Glass Container -->
-    <div class="max-w-[800px] w-full relative z-10 path-glass-container">
+    <div class="max-w-[800px] w-full relative z-10 path-glass-container onb-scroll-container">
       <!-- Header (before DID is retrieved) -->
       <div v-if="!generatedDid" class="text-center flex-shrink-0">
-        <h1 class="text-[26px] font-semibold text-white/96 mb-6 drop-shadow-[0_2px_6px_rgba(0,0,0,0.4)]">
+        <h1 class="text-xl sm:text-2xl md:text-[26px] font-semibold text-white/96 mb-3 sm:mb-6 drop-shadow-[0_2px_6px_rgba(0,0,0,0.4)]">
           Your node's identity
         </h1>
-        <p class="text-[20px] text-white/75 leading-relaxed max-w-[600px] mx-auto mb-6">
+        <p class="text-sm sm:text-base md:text-[20px] text-white/75 leading-relaxed max-w-[600px] mx-auto mb-4 sm:mb-6">
           Your node has a Decentralized Identifier (DID) for secure, passwordless authentication.
         </p>
       </div>