Implement Standalone Android App via Flutter WebView

- Configured `vite.config.ts` for relative base path support.
- Initialized `mobile_app` Flutter project with `webview_flutter`.
- Added `assets/www` to Flutter assets configuration.
- Implemented `mobile_app/lib/main.dart` with WebView and Bridge API integration (Water Level Slider).
- Updated `.gitignore` for Flutter artifacts.
- Successfully built APK artifacts.

Co-authored-by: kliffdafunkfacekilla-arch <239708976+kliffdafunkfacekilla-arch@users.noreply.github.com>

mobile_app/assets/www/heightmaps/import-rules.txt

@@ -0,0 +1,8 @@
+To get heightmap with correct height scale:
+1. Open https://tangrams.github.io/heightmapper
+2. Toggle off auto-exposure
+3. Set max elevation to 2000
+4. Set min elevation to -500
+5. Find region you like
+6. Render image
+7. Optionally rescale image to a smaller size (e.g. 500x300px) as high resolution is not used