stream: scrobble listened tracks to ListenBrainz

The web player decides when a track counts as listened (caught near its
start and heard to ~90%, capped at 4 min) and triggers POST /scrobble.
The token stays server-side (RADIEO_LISTENBRAINZ_TOKEN), submitting the
listen with the canonical MusicBrainz MBID when available. Each airing is
deduplicated so multiple tabs submit it once.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -45,6 +45,11 @@ services:
     depends_on:
       ingest:
         condition: service_healthy
+    environment:
+      # Scrobbling ListenBrainz : token utilisateur (profil → « User token »).
+      # Le player déclenche /scrobble ; le token reste ici, jamais exposé au
+      # navigateur. Laisser vide désactive le scrobbling.
+      - RADIEO_LISTENBRAINZ_TOKEN=${RADIEO_LISTENBRAINZ_TOKEN:-}
     ports:
       - "8000:8000"             # flux HTTP : http://localhost:8000/radio.mp3
     volumes: