feat(discovery): Navidrome AudioMuse-AI client integration and library scoping

Add per-server toggle for AudioMuse-style discovery: Instant Mix via
getSimilarSongs, server similar artists instead of Last.fm on artist pages,
and higher similar-artist count in Now Playing when enabled.

When browsing a single music folder, filter similar/top song results by
album ids from that scope (Navidrome does not apply musicFolderId to those
endpoints). Request larger similar batches under a narrow scope.

Keep radio-from-track as two blocks (shuffled top songs, then shuffled
similar-by-artist) so it differs from Instant Mix. Show Alpha badge beside
the setting. Add research/ to .gitignore.

src/locales/de.ts

@@ -94,6 +94,7 @@ export const deTranslation = {
     addToQueue: 'Zur Warteschlange hinzufügen',
     enqueueAlbum: 'Ganzes Album einreihen',
     startRadio: 'Radio starten',
+    instantMix: 'Instant Mix',
     lfmLove: 'Auf Last.fm liken',
     lfmUnlove: 'Last.fm-Like entfernen',
     favorite: 'Favorisieren',
@@ -396,6 +397,9 @@ export const deTranslation = {
     testBtn: 'Verbindung testen',
     testingBtn: 'Teste…',
     serverCompatible: 'Kompatibel mit: Navidrome · Gonic · Airsonic · Subsonic',
+    audiomuseTitle: 'AudioMuse-AI (Navidrome)',
+    audiomuseDesc:
+      'Aktivieren, wenn dieser Server das AudioMuse-AI-Navidrome-Plugin nutzt. Schaltet Instant Mix pro Titel frei und nutzt ähnliche Künstler vom Server statt Last.fm auf Künstlerseiten.',
     connected: 'Verbunden',
     failed: 'Fehlgeschlagen',
     eqTitle: 'Equalizer',