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-remove-service-tailscale

@@ -5,7 +5,7 @@
 
 tailscale down 2>/dev/null || true
 sudo systemctl disable --now tailscaled.service 2>/dev/null || true
-omarchy-config-shell-bar drop omarchy.tailscale
+omarchy-bar drop omarchy.tailscale
 omarchy-webapp-remove "Tailscale" 2>/dev/null || true
 omarchy-pkg-drop tailscale