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.
Unknown artist resolution now uses the shared metadata source priority and only filters to the sources that can actually participate in this job. Deezer and iTunes remain direct lookup sources, while Hydrabase can now join the title-search path when it is the configured priority source.