feat(radio): add Qobuz artist/track radio with submenu selection

Add /radio/artist and /radio/track Qobuz API endpoints alongside the
existing /radio/album. TrackMenu now shows a radio submenu with QBZ
Radio (RadioPoolBuilder) and Qobuz Radio options when both are
available. Artist header radio button opens a dropdown to choose
between the two engines.

Backend: get_radio_artist(), get_radio_track() in client.rs,
v2_create_qobuz_artist_radio and v2_create_qobuz_track_radio commands.
Frontend: TrackMenu radio submenu with mutual exclusion against
share/download submenus, ArtistDetailView dropdown, LabelView support.
i18n keys added to all four locale files.

src/lib/i18n/locales/fr.json

@@ -1587,6 +1587,9 @@
   },
   "radio": {
     "albumRadio": "Radio de l'album",
-    "creatingAlbumRadio": "Création de la radio de l'album..."
+    "creatingAlbumRadio": "Création de la radio de l'album...",
+    "createRadio": "Créer une radio",
+    "qbzRadio": "Radio QBZ",
+    "qobuzRadio": "Radio Qobuz"
   }
 }