What changed

Widget theme settings (Dark/Light/Custom presets, background transparency, label visibility) were lost after rebooting the device. Previously, configured widgets reverted to "Material You" with full background opacity on the next boot. The selected device profile already survived reboot; now the rest of the configuration does too.

Closes #549

Technical Context

• Root cause: theme was stored in AppWidgetManager.getAppWidgetOptions(). Per AOSP AppWidgetServiceImpl.serializeAppWidget(...), only the five standard OPTION_APPWIDGET_* system keys are written to appwidgets.xml; arbitrary custom keys are silently dropped at boot. Universal Android behavior, not Samsung- or launcher-specific.
• The widget profile survived because it already lived in WidgetSettings' own DataStore, which the system widget service does not touch.
• Fix moves all per-widget configuration (profile + theme) into one JSON-serialized WidgetConfig under widget_config_<id> in the existing widget_preferences DataStore.
• Migration is one-shot per widget, guarded inside the same dataStore.edit {} block as the write so a concurrent save cannot be overwritten by stale legacy data. The legacy options bundle is parsed via a new WidgetTheme.fromLegacyBundleOrNull() that returns null on a system-only bundle — avoiding a false "Material You + 255" migration read.
• Users upgrading without rebooting first keep their existing theme (legacy bundle is still in memory). Users who already lost their theme keep their profile and reconfigure the theme once — it then sticks permanently.
• Verified on a Pixel 8 across a real device reboot: post-boot the widget rendered with the saved Dark theme and configured transparency, and getWidgetConfig(widgetId=15) returned the same values that were saved before the reboot.