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.

config/omarchy/shell.json

@@ -38,6 +38,9 @@
         }
       ],
       "right": [
+        {
+          "id": "omacom.elsewhen"
+        },
         {
           "id": "omarchy.tray"
         },