- Add ThemeMode enum (DEVICE/LIGHT/DARK) with DataStore persistence
- SettingsScreen: appearance section with radio buttons for Device/Light/Dark
- SettingsViewModel: observe and persist theme mode
- MainActivity: read theme setting, apply dark theme, sync status bar icons
- Replace hardcoded Color.White references with MaterialTheme.colorScheme.surface across auth, onboarding, settings, and theme
- Convert AuthVisuals, SettingsVisuals, CloserPalette brushes to @Composable getters using dynamic scheme colors
- Add values-night/themes.xml for dark theme manifest entry
- Add ThemeModeTest unit test for fromStorageValue parsing