Track-level query returning list of albums containing those tracks

There are use cases where it is nice to be able to query beets DB on track level, but show results on album level. Currently, If I use `beet ls -a ...`, then I do see albums only, but the queries involving track fields are ignored. It would be great to see the list of albums in which at least one track matched a track-level query.

Start with the `beet ls -a` command and the query handling for track fields. Trace how matching tracks are converted to album-level results, then verify that an album is listed when at least one of its tracks matches while preserving the existing album-only output behavior.

Written by the indexing model from the issue text.