Install Elsewhen, the world clock plugin, by default

Elsewhen (omacom.elsewhen) arrives as the elsewhen package under
/usr/share/omarchy/plugins, the packaged root the shell scans between its
bundled plugins and the user's. It opens the right section of the default
bar, just before the tray, and a migration installs the package, writes the
widget into a customized shell.json in the same spot, and retires a pristine
pre-package clone of the upstream repo that the package now shadows.

install/omarchy-base.packages

@@ -26,6 +26,7 @@ docker-compose
 dosfstools
 dotnet-runtime
 dua-cli
+elsewhen
 evince
 exfatprogs
 expac