fix(test): the mix-writer test reaches oneCopyPerSong through export_test; suspect fixtures carry the verdict (M498 #5439)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/playlists/song_copies_test.go

@@ -1,4 +1,4 @@
-package playlists
+package playlists_test
 
 import (
 	"context"
@@ -7,6 +7,7 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/playlists"
 )
 
 // A mix holds a song once (M498 #5438) and never a held-back video rip
@@ -30,10 +31,10 @@ func TestOneCopyPerSong_Integration(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	in := []rankedCandidate{
+	in := []playlists.RankedCandidate{
 		{TrackID: single.ID}, {TrackID: rip.ID}, {TrackID: albumCut.ID}, {TrackID: other.ID}, {TrackID: clean.ID},
 	}
-	out, err := oneCopyPerSong(ctx, q, in)
+	out, err := playlists.OneCopyPerSong(ctx, q, in)
 	if err != nil {
 		t.Fatal(err)
 	}