- Add BgUpd + a day-one webview package to PRODUCT_PACKAGES so devices
boot with a working WebView before bg-upd's first check ever runs
- Add config_webview_packages.xml declaring the providers bg-upd can
switch between at runtime
- Add default_wallpaper.png to the framework RRO overlay (single image
for all devices/densities for now — see the new overlay README)