feat(lyrics): make lyrics fully disablable (independent YouLyPlus toggle) (#855)

* feat(lyrics): independent YouLyPlus toggle + all-sources-off state

Replace the binary lyricsMode ('standard' | 'lyricsplus') with an
independent youLyPlusEnabled flag so YouLyPlus and the standard sources
are no longer mutually exclusive — turning one off no longer forces the
other on. YouLyPlus (when on) is tried first with the enabled sources as
fallback; off uses only the enabled sources. When YouLyPlus is off and no
source is enabled, useLyrics fetches nothing (issue #810).

Fresh installs ship with every source off; the rehydrate migration only
restores the old on-by-default set for genuine upgrades, not new installs.

* feat(lyrics): YouLyPlus toggle UI + queue 'no sources' hint

Settings: single YouLyPlus toggle replacing the two mutually exclusive
mode switches; the source list is always visible with a context hint
(fallback vs primary). Queue lyric tab shows a hint when no source is
active. en + de strings; other locales fall back to en.

* docs(changelog): lyrics fully disablable (#855)

CHANGELOG.md

@@ -117,6 +117,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+### Lyrics — sources can be turned off entirely
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), suggested by sddania, PR [#855](https://github.com/Psychotoxical/psysonic/pull/855)**
+
+* YouLyPlus is now an independent toggle instead of an either/or with the standard sources, so lyrics can be switched off completely — turn off YouLyPlus and every source under **Settings → Lyrics**. With nothing selected, no lyrics are fetched or shown and the queue lyric tab says so. Fresh installs start with all sources off.
+
+
+
 ## Fixed
 
 ### In-page browse — virtual scroll and cover-art priority