Full Refresh INSERTs a per-track year (from file tags) into tracks.year, but that column
was only ever in the live INSERT — never in CREATE TABLE and never in a migration. So on
EVERY db (old and current — verified the shipped music_library.db lacks it too) every Full
Refresh track insert hard-failed with 'table tracks has no column named year', importing 0
tracks while artists/albums succeeded.
Fix (additive + nullable, nothing reads it but the writer):
- add year INTEGER to the tracks CREATE TABLE (new DBs)
- ALTER it onto existing tracks tables in _ensure_core_media_schema_columns (the repair
backstop that already runs every init), right beside the file_size repair
Tests (tests/test_tracks_year_migration.py): fresh-DB has it, nullable, idempotent, ALTERs
onto an old year-less table, and a regression that the exact Full Refresh insert fails
before the repair and succeeds after.
