fix(worker): canonicalize bonus-track filenames past the MB tracklist

A track beyond the MusicBrainz tracklist (a Qobuz bonus track) kept streamrip's
raw name (e.g. "13. John Mayer - St. Patrick's Day (Album Version).flac") while
the main tracklist got clean "## Title" names. plan_track_names now canonicalizes
such extras: strip the leading track-number prefix and a leading "<artist> - ",
yielding "13 St. Patrick's Day (Album Version).flac". Requires an explicit
delimiter after the number so titles like "99 Luftballons" are left alone; with
no tracklist resolved at all the on-disk stem is still kept.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/tests/test_mutagen.py

@@ -1,4 +1,34 @@
-from lyra_worker._mutagen import plan_track_names
+from lyra_worker._mutagen import _clean_extra_title, plan_track_names
+
+
+def test_clean_extra_title_strips_number_and_artist_prefix():
+    assert _clean_extra_title(
+        "13. John Mayer - St. Patrick's Day (Album Version)", "John Mayer"
+    ) == "St. Patrick's Day (Album Version)"
+
+
+def test_clean_extra_title_strips_number_without_artist_prefix():
+    assert _clean_extra_title("13. St. Patrick's Day", "John Mayer") == "St. Patrick's Day"
+
+
+def test_clean_extra_title_leaves_plain_title_and_numeric_titles():
+    assert _clean_extra_title("Hidden Track", "John Mayer") == "Hidden Track"
+    # "99 Luftballons" has no delimiter after the number -> not a track-number prefix
+    assert _clean_extra_title("99 Luftballons", "Nena") == "99 Luftballons"
+
+
+def test_plan_canonicalizes_bonus_track_beyond_tracklist():
+    names = [f"{i:02d} Track{i}.flac" for i in range(1, 13)] + [
+        "13. John Mayer - St. Patrick's Day (Album Version).flac"
+    ]
+    tracklist = tuple(f"Track{i}" for i in range(1, 13))
+    plan = plan_track_names(names, tracklist, artist="John Mayer")
+    assert plan[12] == (
+        "13. John Mayer - St. Patrick's Day (Album Version).flac",
+        "13 St. Patrick's Day (Album Version).flac",
+        "St. Patrick's Day (Album Version)",
+        13,
+    )
 
 
 def test_plan_uses_tracklist_titles_and_numbers():