feat: MVP implementation - Kiosk Browser

- Fullscreen WebView with immersive mode
- URL whitelist system
- Admin PIN-protected settings
- Boot receiver for auto-launch
- Idle timeout with homepage reset
- Lock Task Mode support
- Material Design 3 UI

Team: Pluto (coordinator), Margaret, Spirit

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties