detect_album_info_web gains a last-resort step: when a track matched a SINGLE
with no usable album context, look up the parent ALBUM that contains it (via
get_artist_albums_for_source + get_artist_album_tracks) and promote to it, so it
groups with its album-mates and gets the album's cover instead of the single's.
GATED behind metadata_enhancement.single_to_album (default OFF) — it's a
per-import metadata lookup, so it's opt-in, matching the canonical-version
pattern. Fully fail-safe: flag off, no source, or any client error/miss -> None,
so the track stays exactly as matched (never worse than today). The promoted
album name is forced past get_import_clean_album (which otherwise pins the
single's name) so grouping + tags use the album. 4 glue seam tests added
(promote-when-enabled, disabled-by-default, no-match, client-raises); 462
import-suite tests pass.
58363ae510