feat: the duplicates review says what each match rests on and plays every copy (#6168)

Each group now states its evidence: identical audio data, or the share of
audio fingerprints that agree. Copies titled as different songs in one
acoustic group say so and ask the reviewer to listen, and each copy has a
play button so they can.

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

internal/api/admin_duplicates.go

@@ -22,6 +22,7 @@ import (
 type duplicateMemberView struct {
 	TrackID     string `json:"track_id"`
 	Title       string `json:"title"`
+	ArtistID    string `json:"artist_id"`
 	ArtistName  string `json:"artist_name"`
 	AlbumID     string `json:"album_id"`
 	AlbumTitle  string `json:"album_title"`
@@ -34,6 +35,9 @@ type duplicateMemberView struct {
 	PlayCount   int64  `json:"play_count"`
 	DiscNumber  *int32 `json:"disc_number"`
 	TrackNumber *int32 `json:"track_number"`
+	// StreamURL lets the review play each copy, to hear whether they are the
+	// same song (#6168).
+	StreamURL string `json:"stream_url"`
 }
 
 // duplicateGroupView is one proposal. SurvivorTrackID and SurvivorReason are
@@ -277,6 +281,7 @@ func foldDuplicateGroups(rows []dbq.ListPendingDuplicateGroupMembersRow) []dupli
 		groups[n].Members = append(groups[n].Members, duplicateMemberView{
 			TrackID:     trackID,
 			Title:       row.Title,
+			ArtistID:    uuidToString(row.ArtistID),
 			ArtistName:  row.ArtistName,
 			AlbumID:     uuidToString(row.AlbumID),
 			AlbumTitle:  row.AlbumTitle,
@@ -289,6 +294,7 @@ func foldDuplicateGroups(rows []dbq.ListPendingDuplicateGroupMembersRow) []dupli
 			PlayCount:   row.PlayCount,
 			DiscNumber:  row.DiscNumber,
 			TrackNumber: row.TrackNumber,
+			StreamURL:   streamURL(row.TrackID),
 		})
 		candidates[n] = append(candidates[n], library.SurvivorCandidate{
 			TrackID: trackID, FileFormat: row.FileFormat, FileSize: row.FileSize, AddedAt: row.AddedAt.Time,