Let the Elsewhen migration carry on without a shell to ask

A bare `omarchy-shell shell rescanPlugins` exits 1 when no shell answers on the caller's tree, and omarchy-migrate runs migrations under `set -e`, so an update run from a TTY or over ssh, or one whose shell had gone down while the package replaced its QML, died at "omarchy-shell is not running" before its post-update hooks, shell restart and reboot prompt, and re-failed the same way every time until a shell could be asked. The rescan is now best-effort, like `omarchy-bar put` already is and like #11117 makes the plugin commands' closing rescan: the update restarts the shell once the migrations are through, and a session without one has no bar to place on. An unknown widget on a live shell still leaves the migration pending.

migrations/1789581661.sh

@@ -10,5 +10,7 @@ if [[ ! $OMARCHY_PATH -ef /usr/share/omarchy && -d $packaged_plugin && ! -e $use
   ln -s "$packaged_plugin" "$user_plugin"
 fi
 
-omarchy-shell shell rescanPlugins
+# Best-effort, like the put below: an update whose shell cannot be asked still
+# finishes, and restarts the shell once the migrations are through.
+omarchy-shell -q shell rescanPlugins
 omarchy-bar put omacom.elsewhen --before omarchy.clock