The Arrangement Editor plugin was only reachable via the generic Plugins
gallery. Give it a dedicated sidebar entry (Library group, below Songs)
through the existing PROMOTED_PLUGINS mechanism in shell.js — a NAV entry,
a promoted slot anchored after "songs", and an edit icon.
renderPromotedNav already gates each promoted slot on the plugin being
present in /api/plugins, so the entry shows only when the editor is
installed. The displayed label comes from the plugin manifest's nav.label.
Signed-off-by: topkoa <topkoa@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
