feat(android): file upload/download + in-app tab redesign

Companion WebView now supports file inputs and downloads, and apps
opened in the in-app tab get a proper loading splash and a footer
control bar matching the web app-session bar.

- onShowFileChooser wired to an ActivityResultLauncher so <input
  type=file> opens the system file browser (kiosk + in-app tab)
- DownloadListener: http(s) via DownloadManager (forwarding session
  cookies), blob: via JS->base64->MediaStore, data: decoded inline
- in-app tab: app-icon + progress loading splash (eager favicon
  fetch, upgraded via onReceivedIcon)
- footer controls (back/forward/refresh/open/close) matched to the
  web AppSession mobile bar, with the same SVG glyphs as drawables
- bump to 0.4.8 (versionCode 12)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Android/app/src/main/res/values/strings.xml

@@ -23,6 +23,9 @@
     <string name="remote_input_hint">Use your phone as a keyboard and mouse for the kiosk</string>
     <string name="close">Close</string>
     <string name="open_in_browser">Open in browser</string>
+    <string name="back">Back</string>
+    <string name="forward">Forward</string>
+    <string name="refresh">Refresh</string>
     <string name="server_name_label">Server Name (optional)</string>
     <string name="server_name_placeholder">My Archipelago</string>
 </resources>