fix(worker): trust the requested artist when it's in the file path (stop MP3-over-FLAC)

Confidence scoring read the artist from the immediate folder as "Artist - Album", so
common FLAC rip layouts — artist in a parent folder ("Rihanna\(2009) Rated R\…") or
buried ("2009 - Rihanna - Rated R") — parsed with no/garbage artist and scored below
the 0.7 gate. Real FLACs got filtered out and a clean-named MP3 (0.88) won, so Lyra
downloaded lossy when lossless was available (Rihanna "Rated R": 8 FLACs all <0.5).

_parse_search_responses now takes the requested artist and, when it appears anywhere
in the candidate's path (via _path_matches), sets it as the candidate artist so
confidence reflects reality. Especially helps blocklisted-artist fallbacks, whose
album-only results come from varied folder structures. 337 tests pass.

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

worker/tests/test_slskd_cancel.py

@@ -110,6 +110,27 @@ def test_parse_ranks_free_and_fast_peers_first():
     assert peers == ["fast", "slow", "queued"]  # free+fast first; no-slot peer last despite speed
 
 
+def test_parse_uses_requested_artist_when_present_in_path():
+    # Real "Rated R" MP3-over-FLAC bug: the artist is in a PARENT folder ("Rihanna\(2009) Rated
+    # R\…"), so the "Artist - Album" folder parse yields no artist and confidence tanks. When the
+    # requested artist is in the path, trust it so the candidate scores as Rihanna.
+    responses = [
+        {"username": "p", "hasFreeUploadSlot": True, "uploadSpeed": 1000, "queueLength": 0,
+         "files": [{"filename": r"@@x\Music\Rihanna\(2009) Rated R\01. Mad House.flac", "size": 5}]},
+    ]
+    c = _parse_search_responses(responses, artist="Rihanna")[0]
+    assert c["artist"] == "Rihanna"
+
+
+def test_parse_without_artist_falls_back_to_folder_parse():
+    responses = [
+        {"username": "p", "hasFreeUploadSlot": True, "uploadSpeed": 1000, "queueLength": 0,
+         "files": [{"filename": r"x\Some Band - Some Album\01.flac", "size": 5}]},
+    ]
+    c = _parse_search_responses(responses)[0]  # no artist arg → folder parse
+    assert c["artist"] == "Some Band"
+
+
 def test_parse_prefers_shorter_transfer_over_raw_speed():
     # The Hybrid Theory case: a peer advertising higher speed but serving a ~2x-larger rip (24-bit
     # / bloated FLAC) should lose to a peer with lower speed but a smaller standard rip that