Tacobell444: when tracks land in an album across multiple batches (a wishlist
run, the Album Completeness job, a missed track re-downloaded later), the folder
is rebuilt from API metadata each time — so when $albumtype or $year come back
blank/different on a later batch, the folder NAME changes and the album splits,
forcing a Reorganize.
Fix: build_final_path_for_track now checks whether the album already lives in a
single folder on disk and, if so, drops the new track there instead of a freshly
templated folder. Match (chosen): exact stored Spotify album id first, then a
STRICT >=0.85 name+artist match (vs the 0.7 used elsewhere) — a wrong match here
misplaces a file. New core/library/existing_album_folder.resolve_existing_album_folder
holds the logic; always-on with template fallback.
Safety rails: only returns a folder UNDER the transfer dir (never a read-only
library/NAS mount), only when the album lives in EXACTLY ONE folder (multiple =
disc subfolders, which DatabaseTrack can't disambiguate — those defer to the
template), and any failure falls through to the template path. Added
MusicDatabase.get_album_by_spotify_album_id for the id-first lookup.
Tests: single-folder reuse, no-match, below-threshold, multi-folder defer,
outside-transfer reject, id-first, missing transfer dir, no-files-on-disk.
8 tests; 1556 path/import/download tests pass (only the known soundcloud
failures remain).
