New /library: GET /api/library lists LibraryItems enriched with rgMbid + year
from the matching MonitoredRelease. Client renders a cover-art grid with a live
filter; clicking an album opens the AlbumModal (tracklist). Added Library to the
nav. The album-only overview to see everything downloaded.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Jonathan