feat: notifications say what changed and alert once: a grouped notice names the tracks, grows without re-alerting, and a phone pile lists its titles (M542 #6146-#6151)

- An update to a grouped notice keeps its arrival time and email state, so the
  phone and the email no longer go off again each time it grows.
- Notices carry the names of what changed (newest ten), shown as three and
  "and N more": tracks still missing after the scan's move/replacement fold,
  duplicate groups new to a sweep, songs merged automatically, and the track
  and listener a playback error was for.
- Duplicates found counts only the groups new to that sweep; playback errors
  count reports, not the unresolved total.
- A scan failure says what stopped and links to Admin > Library.
- Android: a pile of more than three alerts lists the newest five titles.

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

internal/api/notify_producers.go

@@ -6,6 +6,7 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/notifications"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/requests"
 )
@@ -66,21 +67,19 @@ func (h *handlers) trackLabel(ctx context.Context, trackID pgtype.UUID) string {
 	if err != nil {
 		return ""
 	}
-	if a, aerr := q.GetArtistByID(ctx, t.ArtistID); aerr == nil && a.Name != "" {
-		return a.Name + " – " + t.Title
+	if a, aerr := q.GetArtistByID(ctx, t.ArtistID); aerr == nil {
+		return library.TrackLabel(a.Name, t.Title)
 	}
 	return t.Title
 }
 
-// notifyPlaybackErrors tells admins how many playback errors await review.
-// The notice coalesces, so while it is unread a new report only updates the
-// count.
-func (h *handlers) notifyPlaybackErrors(ctx context.Context) {
-	n, err := dbq.New(h.pool).CountUnresolvedPlaybackErrors(ctx)
-	if err != nil {
-		h.logger.Warn("api: playback_error: count unresolved", "err", err)
-		return
+// notifyPlaybackErrors tells admins a track failed to play, naming it and who
+// it failed for (M542). The notice coalesces: while it is unread each report
+// adds one to its count and its name to the front of the list.
+func (h *handlers) notifyPlaybackErrors(ctx context.Context, trackID pgtype.UUID, user dbq.User) {
+	p := notifications.Payload{Count: 1}
+	if name := h.trackLabel(ctx, trackID); name != "" {
+		p.Items = []string{name + " (" + userLabel(user) + ")"}
 	}
-	h.notifier.NotifyLogged(ctx, notifications.KindPlaybackErrors, notifications.ToAdmins(pgtype.UUID{}),
-		notifications.Payload{Count: n}.Map())
+	h.notifier.NotifyLogged(ctx, notifications.KindPlaybackErrors, notifications.ToAdmins(pgtype.UUID{}), p.Map())
 }