feat(app): mobile improvements — native-feel viewport, keyboard, HIG tabs, PWA fix

- Lock viewport: position:fixed on html/body prevents iOS bounce scroll
- No zoom on input focus: maximum-scale=1, user-scalable=no
- Keyboard-responsive chat: visualViewport API detects keyboard, hides
  tab bar, scrolls chat to bottom, scrollIntoView on input focus
- iOS HIG tab bar: 49pt height, vertical icon+label, safe-area-inset-bottom
- PWA fix: manifest start_url/scope/id changed from '/' to './' for
  subpath deployment compatibility
- PlayerBar: variant prop (fixed/inline), inline on mobile above tab bar,
  fixed on desktop. No more overlap with tab bar.

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

packages/app/vite.config.ts

@@ -25,7 +25,7 @@ export default defineConfig({
       registerType: 'autoUpdate',
       includeAssets: ['favicon.svg', 'icon.svg', 'apple-touch-icon-180x180.png'],
       manifest: {
-        id: '/',
+        id: './',
         name: 'AIUI',
         short_name: 'AIUI',
         description: 'AI chat interface with rich content surfaces',
@@ -34,8 +34,8 @@ export default defineConfig({
         display: 'standalone',
         display_override: ['standalone', 'minimal-ui'],
         orientation: 'any',
-        start_url: '/',
-        scope: '/',
+        start_url: './',
+        scope: './',
         icons: [
           {
             src: 'pwa-192x192.png',