feat: a version named after a dash counts as a version, and a song held twice beside a wrong slot no longer blocks it (M498)

- songKey drops a dashed version suffix (" - Instrumental Version", " - Radio
  Edit", live, remix, mix, acoustic, demo, reprise, rework, VIP), so Andora's
  "Goodbye Yesterday - Instrumental Version" is distinct, not a wrong slot.
- wrongSlots accepts several fitting copies when they share one title
  (Killjoy twice beside Dreamland): the other slot's copy is removed, and the
  doubled song is left for the next sweep to find as a pair the resolver merges.

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

internal/library/duplicate_classify_test.go

@@ -28,6 +28,10 @@ func TestClassifyDuplicateGroup(t *testing.T) {
 			[]ClassifyMember{m("moe", "Lovesick"), m("moe", "Lovesick (Instrumental)")}, ClassDistinct},
 		{"Void: one album, one audio under three song titles", "acoustic",
 			[]ClassifyMember{m("void", "Slimewar (into the void)"), m("void", "Void"), m("void", "Reach")}, ClassMismatch},
+		{"a version named after a dash", "acoustic",
+			[]ClassifyMember{m("andora", "Goodbye Yesterday"), m("andora", "Goodbye Yesterday - Instrumental Version")}, ClassDistinct},
+		{"a dash that names no version", "acoustic",
+			[]ClassifyMember{m("a", "Monday Chill - Part One"), m("a", "Monday Chill - Part Two")}, ClassMismatch},
 		{"Slasher and Slasher II are not versions of one song", "acoustic",
 			[]ClassifyMember{m("slasher", "Slasher"), m("slasher", "Slasher II")}, ClassMismatch},
 		{"Big Me: the single and the album", "exact",
@@ -90,6 +94,11 @@ func TestWrongSlots(t *testing.T) {
 		{"Void: the file is Void's; the other two slots are other songs", copies("Slimewar (into the void)", "Void", "Reach"), void, 1, []int{0, 2}, true},
 		{"no track list", copies("Void", "Reach"), nil, -1, nil, false},
 		{"a title the track list does not hold", copies("Void", "Bonus"), void, -1, nil, false},
+		{"Killjoy held twice beside Dreamland's slot", []slotCopy{
+			{Title: "Dreamland", Artist: "Fox Stevenson", DurationMs: 167000},
+			{Title: "Killjoy", Artist: "Fox Stevenson", DurationMs: 167000},
+			{Title: "Killjoy", Artist: "Fox Stevenson", DurationMs: 166000},
+		}, []dbq.MbReleaseTrack{track("Killjoy", 166500), track("Dreamland", 214000)}, 1, []int{0}, true},
 		{"two slots fit the file", copies("Void", "Reach"), []dbq.MbReleaseTrack{track("Void", 220000), track("Reach", 221500)}, -1, nil, false},
 		{"a slot near but not within the fit", copies("Void", "Reach"), []dbq.MbReleaseTrack{track("Void", 220000), track("Reach", 226000)}, -1, nil, false},
 		{"no slot fits", copies("Reach", "Slimewar (into the void)"), void, -1, nil, false},