8 test files had _DummyConfigManager missing get_active_media_server(),
causing failures when pytest ran them before the test file that had it.
Whichever file set sys.modules first won, and the incomplete dummy broke
later tests. Also fix script.js read_text() missing encoding='utf-8'
which failed on non-UTF-8 default locales.
Repair-worker album fills now generate explicit track IDs when copying rows, instead of relying on SQLite auto-assignment that no longer exists for TEXT primary keys. The unknown-artist fixer now does the same for new artists.
Also add a regression test for the album-fill copy branch and keep the AcoustID scanner resilient to legacy null-ID rows.
