Rust export_image(filename,base64,action) + read_file_base64(path) (registered).
Kotlin exportimg: branch — base64-decode, then SAF-save the PNG (CreateDocument
image/png) or share it via FileProvider + ACTION_SEND chooser. Settings gets a
'Фон для картинки' row: pick a photo (pickLocalFile image/*), read it as base64,
downscale to <=1080 and store as a data URL in localStorage for the 'С фото'
variant. Rust compiles in tauri dev; native paths need an APK rebuild to test.