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.

docs/omarchy-shell.md

@@ -88,6 +88,19 @@ bar from the CLI — `use | reset | defaults | position | transparent | put |
 move | set`, with placement flags such as `--section` and `--index`.
 The lower-level IPC methods remain available through `omarchy-shell shell ...`.
 
+## Packaged plugins
+
+A default plugin can ship as its own Arch package instead of in the Omarchy
+checkout: Elsewhen (`omacom.elsewhen`) is the `elsewhen` package. pacman installs them at
+`/usr/share/omarchy/plugins/<id>/`, a root the shell scans between
+`$OMARCHY_PATH/shell/plugins` and `~/.config/omarchy/plugins`. A packaged
+`omarchy.*` id is trusted like a bundled plugin and loads by default; any other
+packaged id behaves like an installed plugin. Precedence is bundled, then
+packaged, then user, so a checkout under `omarchy dev link` overrides the
+package. Packaged plugins update through `omarchy update` and leave through
+pacman; `omarchy plugin update` and `omarchy plugin remove` refuse them and
+name the package, and Setup › Plugins › Remove does not list them.
+
 ## IPC
 
 The shell exposes a `shell` target (the host also registers