Rebuild Kotlin Android app for mobile UX and add CI workflow

[darrenintr]

Motivation

• Provide a mobile-first Kotlin Android wrapper that preserves the existing web product while giving a native app-like experience on phones.
• Add an automated build workflow so APKs are produced on repository changes to the Android app.

Description

• Reworked MainActivity.kt to add bottom navigation, pull-to-refresh (SwipeRefreshLayout), a top loading progress bar, tuned WebView settings and a custom user-agent for mobile behavior.
• Replaced the main layout with activity_main.xml that includes the progress bar, SwipeRefreshLayout wrapped WebView, and a BottomNavigationView, and added res/menu/bottom_navigation_menu.xml with navigation items and updated res/values/strings.xml labels.
• Added the androidx.swiperefreshlayout:swiperefreshlayout:1.1.0 dependency in app/build.gradle.kts and updated the Kotlin app README.md to document the mobile UX and CI.
• Added a GitHub Actions workflow at .github/workflows/android-kotlin-ci.yml that builds debug and release APKs and uploads artifacts when mobile/kotlin-app/** changes.

Testing

• Attempted to run ./gradlew tasks --all in mobile/kotlin-app, which failed because the repository does not include the Gradle wrapper script (./gradlew: No such file or directory).
• No CI jobs were executed in this environment; the added workflow is configured to run on push/PR and will build APKs when executed in GitHub Actions.

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Codex Task