feat(i18n): add album cover context menu translations

Keys for add/change/remove custom cover, open in browser,
save as, and toast messages. All 4 locales (en, es, de, fr).

cc

src/lib/i18n/locales/de.json

@@ -219,7 +219,15 @@
     "addToPlaylist": "Zur Playlist hinzufügen",
     "makeAvailableOffline": "Für offline verfügbar machen",
     "makeAllAvailableOffline": "Alles für offline verfügbar machen",
-    "disc": "Disc"
+    "disc": "Disc",
+    "addCover": "Benutzerdefiniertes Albumcover hinzufügen",
+    "changeCover": "Benutzerdefiniertes Albumcover ändern",
+    "removeCover": "Benutzerdefiniertes Albumcover entfernen",
+    "openInBrowser": "Im Browser öffnen",
+    "saveAs": "Speichern unter...",
+    "customCoverSet": "Albumcover aktualisiert",
+    "customCoverRemoved": "Benutzerdefiniertes Albumcover entfernt",
+    "customCoverError": "Fehler beim Aktualisieren des Albumcovers"
   },
   "artist": {
     "albums": "Alben",

src/lib/i18n/locales/en.json

@@ -231,7 +231,15 @@
     "makeAvailableOffline": "Make available offline",
     "makeAllAvailableOffline": "Make all available offline",
     "disc": "Disc",
-    "loadError": "Could not load album tracks. Please try again."
+    "loadError": "Could not load album tracks. Please try again.",
+    "addCover": "Add custom album cover",
+    "changeCover": "Change custom album cover",
+    "removeCover": "Remove custom album cover",
+    "openInBrowser": "Open in browser",
+    "saveAs": "Save as...",
+    "customCoverSet": "Album cover updated",
+    "customCoverRemoved": "Custom album cover removed",
+    "customCoverError": "Failed to update album cover"
   },
   "artist": {
     "albums": "Albums",

src/lib/i18n/locales/es.json

@@ -231,7 +231,15 @@
     "makeAvailableOffline": "Disponible offline",
     "makeAllAvailableOffline": "Todo disponible offline",
     "disc": "Disco",
-    "loadError": "No se pudieron cargar las pistas del album. Intenta de nuevo."
+    "loadError": "No se pudieron cargar las pistas del album. Intenta de nuevo.",
+    "addCover": "Agregar portada personalizada",
+    "changeCover": "Cambiar portada personalizada",
+    "removeCover": "Eliminar portada personalizada",
+    "openInBrowser": "Abrir en navegador",
+    "saveAs": "Guardar como...",
+    "customCoverSet": "Portada del album actualizada",
+    "customCoverRemoved": "Portada personalizada eliminada",
+    "customCoverError": "Error al actualizar la portada"
   },
   "artist": {
     "albums": "Álbumes",

src/lib/i18n/locales/fr.json

@@ -219,7 +219,15 @@
     "addToPlaylist": "Ajouter à la playlist",
     "makeAvailableOffline": "Rendre disponible hors ligne",
     "makeAllAvailableOffline": "Rendre tout disponible hors ligne",
-    "disc": "Disque"
+    "disc": "Disque",
+    "addCover": "Ajouter une pochette personnalisée",
+    "changeCover": "Changer la pochette personnalisée",
+    "removeCover": "Supprimer la pochette personnalisée",
+    "openInBrowser": "Ouvrir dans le navigateur",
+    "saveAs": "Enregistrer sous...",
+    "customCoverSet": "Pochette de l'album mise à jour",
+    "customCoverRemoved": "Pochette personnalisée supprimée",
+    "customCoverError": "Erreur lors de la mise à jour de la pochette"
   },
   "artist": {
     "albums": "Albums",