v1.26.0 — One track per artist per game

One track per artist per game (#57)

Reported by a player who kept seeing the same bands session after session.

• A game now plays at most one track per artist, including the per-player
  artist-boost rounds. If two players pick the same band, only one round comes
  from it — the second player's boost comes from another of their picks rather
  than being lost.
• Featured credits and reversed names fold onto the same act, so
  Nirvana Feat. … and Nirvana, or Beatles, The and The Beatles, count as
  one artist.
• Small libraries keep working. If the eligible pool has fewer distinct
  artists than the game has rounds, repeats are still allowed — a game that
  refuses to start would be worse than a repeated artist.

If your library is large, note that the general pool was rarely the culprit: on a
12,000-track pool, plain random selection yields a given popular artist about
once every sixteen 10-round games. The per-player artist picks were the real
driver of "the same bands every session", which is what this release changes.

Weighting selection against recent games is tracked separately in #73.

No database, configuration or API changes. Decoy answers are unaffected.

Also in this release: the image build workflow moved to current GitHub Actions
versions (no functional change).

Docker images for this release are published to GHCR and Docker Hub.