Replaces the string-embedded `character:Name (Fandom)` naming scheme with
structural storage: bare name in tag.name, kind in kind column only,
fandom association via fandom_id. Extends to all tag kinds — the kind
prefix (`artist:`, `fandom:`, etc.) is stripped from tag.name repo-wide,
making tag.name authoritative display text and tag.kind the sole source
of truth for kind.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
