Split omarchy-plugin into siblings and consolidate bar config into omarchy-bar

omarchy-plugin mixed plugin lifecycle, clone/edit, and bar-layout mutation.
The bar layout was mutated by two separate engines (an embedded Python
mutate_bar here and jq in omarchy-config-shell-bar), each with its own
manifest walker.

- omarchy-plugin is now a ~220-line router; clone and edit move to
  omarchy-plugin-clone and omarchy-plugin-edit, matching the existing
  plugin-{source,add,update,remove,available,validate,scan} sibling pattern
- omarchy-config-shell-bar is replaced by omarchy-bar, the single bar engine
  (show/layout/list/options/use/reset/add/move/remove/set/replace/position/
  transparent/settings) with one jq pipeline; the Python mutate_bar and its
  python3 dependency are gone
- omarchy-plugin-catalog is the shared manifest scanner used by omarchy-bar
  (widget/option enumeration, add validation) and omarchy-plugin-clone
  (source enumeration), replacing three find|jq re-implementations
- service install/remove and refresh-shell call omarchy-bar; docs and tests
  updated to the new command surface

bin/omarchy-install-service-tailscale

@@ -14,6 +14,6 @@ echo -e "\nAllowing $USER to manage Tailscale..."
 sudo tailscale set --operator="$USER"
 
 echo -e "\nAdding Tailscale to the bar..."
-omarchy-config-shell-bar add omarchy.tailscale
+omarchy-bar add omarchy.tailscale
 
 omarchy-webapp-install "Tailscale" "https://login.tailscale.com/admin/machines" https://cdn.jsdelivr.net/gh/homarr-labs/dashboard-icons/png/tailscale-light.png