Adds the model + MeApi.systemPlaylistsStatus() for the home Playlists
row's placeholder-variant logic (building / failed / pending /
seed-needed). Mirrors GET /api/me/system-playlists-status which
returns the caller's most recent system_playlist_runs row.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
