feat(webui): add PWA support for mobile home screen installation

- Add manifest.json with icons for install prompt
- Add service worker with cache-first for static assets
- Register SW in main.tsx
- Link manifest in index.html

webui/index.html

@@ -14,6 +14,7 @@
     <link rel="icon" type="image/svg+xml" href="/brand/nanobot_mark.svg" />
     <link rel="alternate icon" type="image/png" sizes="32x32" href="/brand/nanobot_favicon_32.png" />
     <link rel="apple-touch-icon" sizes="180x180" href="/brand/nanobot_apple_touch.png" />
+    <link rel="manifest" href="/manifest.json" />
     <style>
       html,
       body,