Completes playlist CRUD. The detail header shows an edit button only
for the user's own playlists (is-owner = the open id is in the sidebar
list); it opens an EditPlaylistModal:
- Save -> update_playlist (rename); refreshes the detail header name
and the sidebar list.
- Delete -> delete_playlist; closes the modal, navigates back, and
refreshes the sidebar.
Adds the pen-line icon (Lucide) used by the edit button.
cc