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/build.gradle.kts

@@ -11,8 +11,8 @@ android {
         applicationId = "com.archipelago.app"
         minSdk = 26
         targetSdk = 35
-        versionCode = 10
-        versionName = "0.4.6"
+        versionCode = 12
+        versionName = "0.4.8"
 
         vectorDrawables {
             useSupportLibrary = true