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)

src/store/authLyricsSettingsActions.ts

@@ -15,14 +15,14 @@ export function createLyricsSettingsActions(set: SetState): Pick<
   | 'setLyricsServerFirst'
   | 'setEnableNeteaselyrics'
   | 'setLyricsSources'
-  | 'setLyricsMode'
+  | 'setYouLyPlusEnabled'
   | 'setLyricsStaticOnly'
 > {
   return {
     setLyricsServerFirst: (v) => set({ lyricsServerFirst: v }),
     setEnableNeteaselyrics: (v) => set({ enableNeteaselyrics: v }),
     setLyricsSources: (sources) => set({ lyricsSources: sources }),
-    setLyricsMode: (v) => set({ lyricsMode: v }),
+    setYouLyPlusEnabled: (v) => set({ youLyPlusEnabled: v }),
     setLyricsStaticOnly: (v) => set({ lyricsStaticOnly: v }),
   };
 }