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/authStoreRehydrate.ts

@@ -40,10 +40,13 @@ export function computeAuthStoreRehydration(state: AuthState): Partial<AuthState
       : {};
 
   // Migrate lyricsServerFirst + enableNeteaselyrics → lyricsSources (one-time).
+  // Only for an *existing* persisted state (upgrade from a build without
+  // lyricsSources). Fresh installs have no persisted state → keep the
+  // all-off default (issue #810); don't resurrect the old on-by-default set.
   let lyricsSourcesMigrated: { lyricsSources?: LyricsSourceConfig[] } = {};
   try {
     const raw = JSON.parse(localStorage.getItem('psysonic-auth') ?? '{}') as { state?: Record<string, unknown> };
-    if (!raw?.state?.lyricsSources) {
+    if (raw?.state && !raw.state.lyricsSources) {
       const serverFirst = (raw?.state?.lyricsServerFirst as boolean | undefined) ?? true;
       const neteaseOn   = (raw?.state?.enableNeteaselyrics as boolean | undefined) ?? false;
       const migrated: LyricsSourceConfig[] = serverFirst
@@ -53,6 +56,16 @@ export function computeAuthStoreRehydration(state: AuthState): Partial<AuthState
     }
   } catch { /* ignore */ }
 
+  // Migrate legacy `lyricsMode` ('standard' | 'lyricsplus') → `youLyPlusEnabled`
+  // (one-time). Existing users keep YouLyPlus on iff they were on lyricsplus
+  // mode; the legacy field is then stripped so it doesn't sit as cruft.
+  let youLyPlusMigrated: { youLyPlusEnabled?: boolean } = {};
+  const legacyLyricsMode = (state as { lyricsMode?: unknown }).lyricsMode;
+  if (legacyLyricsMode === 'lyricsplus' || legacyLyricsMode === 'standard') {
+    youLyPlusMigrated = { youLyPlusEnabled: legacyLyricsMode === 'lyricsplus' };
+  }
+  delete (state as { lyricsMode?: unknown }).lyricsMode;
+
   // One-time: older builds could persist smooth=false as the default. Force smooth on once
   // so updates do not leave users on discrete scrolling; after this flag exists, only an
   // explicit toggle in Settings may turn it off (persisted in psysonic-auth).
@@ -145,6 +158,7 @@ export function computeAuthStoreRehydration(state: AuthState): Partial<AuthState
     loudnessPreIsRefV1: true,
     ...conflictingLegacyState,
     ...lyricsSourcesMigrated,
+    ...youLyPlusMigrated,
     ...wheelSmoothOneTime,
     ...seekbarStyleMigrated,
     ...queueDurationDisplayModeMigrated,