Adds a boot-time goroutine that walks albums with NULL mbid, re-reads
tags from one track per album via dhowden/tag, and persists album + artist
MBIDs. Healed albums also get their cover_art_source='none' cleared so the
enricher's next batch retries the MBCAA fetch. Caps at 5000 albums per
boot to avoid stalling startup on huge libraries.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bvandeusen