fix(library): always split comma-separated artists even if glued name exists

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

services/api/internal/library/meta/meta_test.go

@@ -33,6 +33,8 @@ func TestSplitArtists(t *testing.T) {
 	assert.Equal(t, []string{"main:Tom", "main:Jerry"}, names(SplitArtists("Tom & Jerry", known)))
 	assert.Equal(t, []string{"main:A", "main:B"}, names(SplitArtists("A; B", nil)))
 	assert.Equal(t, []string{"main:A", "main:B", "main:C"}, names(SplitArtists("A, B, C", nil)))
+	assert.Equal(t, []string{"main:A", "main:B"}, names(SplitArtists("A, B", func(string) bool { return true })), "already glued name is still split")
+	assert.Equal(t, []string{"main:Tyler, the Creator"}, names(SplitArtists("Tyler, the Creator", nil)))
 	assert.Equal(t, []string{"main:A", "feat:B", "feat:C"}, names(SplitArtists("A feat. B & C", nil)))
 	assert.Equal(t, []string{"main:A"}, names(SplitArtists("A / a", nil)), "duplicates by key are dropped")
 	assert.Empty(t, SplitArtists("  ", nil))