Fallback priority for lastgenre

[freitagdavid]

Hi! I looked through issues/discussions and couldn’t find anything matching this.

Problem

lastgenre currently uses a single configured source (e.g. track, album, or artist) to fetch tags from Last.fm. In practice, track/album pages are sometimes missing (or return no tags), even when the artist page has usable tags. This can cause genres to fall back to the configured fallback more often than necessary.

Proposed improvement

Add an optional config option to try multiple sources in priority order until a valid genre is found:

lastgenre:
  source_priority:
    - album
    - track
    - artist

Desired behavior

When running lastgenre:

1. Try album. If it returns tags that survive existing filtering/whitelist/min-count/etc, use the result.
2. Otherwise try track, then artist in order.
3. Only use fallback if none of the sources produce an acceptable genre.

Notes / edge cases

• I’m thinking “no genre returns” should include both:
• no tags found, and
• tags found but all filtered out by existing rules.
• If source_priority is not set, keep current behavior (single source).

If it sounds reasonable, I’m happy to take a stab at a PR.