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>

ingest/radieo/api.py

@@ -46,6 +46,12 @@ def annotate_uri(path: Path, track: Track) -> str:
         # stream so the player can show a discreet source indicator.
         f'origin="{esc(track.origin)}"',
     ]
+    # Canonical MusicBrainz recording MBID when the Canonicalizer found one.
+    # Surfaced on the stream so listeners can scrobble the exact recording to
+    # ListenBrainz (see stream/web.liq /scrobble). Passed explicitly rather than
+    # relying on Liquidsoap re-reading the file tags, which is format-dependent.
+    if track.mbid:
+        fields.append(f'musicbrainz_trackid="{esc(track.mbid)}"')
     # Web page the track was pulled from, so the player can link back to the
     # source (see Track.page_url for how it's derived per backend).
     if track.page_url is not None: