Add Android WebView client (android-client/) ...

Thin Android shell that loads the Navi web interface from a configured
server URL. All UI served from the server — no local assets, no rebuild
needed for interface updates.

Features:
- First-launch setup screen to enter server URL (stored in SharedPreferences)
- On connection error: clears saved URL so next launch re-asks
- Full-screen WebView, no toolbar
- Camera + gallery + file picker via WebChromeClient.onShowFileChooser
- HTTP cleartext enabled for local network access
- targetSdk 34 to avoid forced edge-to-edge on Android 15
- Adaptive icon: logo SVG converted to Android vector drawable

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