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/notifications/kinds.go

@@ -69,12 +69,9 @@ func (c Channels) Effective() Channels {
 type spec struct {
 	audience Audience
 	// coalesce: while one of these is unread, a new event updates it in place
-	// rather than adding a row. For the burst-prone admin kinds.
+	// rather than adding a row. For the burst-prone admin kinds. Each event
+	// is "N more", so the update adds its count and names to the row's.
 	coalesce bool
-	// sumCount: a coalesced update adds the payload's `count` to the unread
-	// row's, because each event is "N more". Without it the newer payload
-	// replaces the older, because each event states the whole current total.
-	sumCount bool
 	group    EmailGroup
 	defaults Channels
 }
@@ -88,16 +85,15 @@ var (
 )
 
 var specs = map[Kind]spec{
-	KindRequestApproved:   {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
-	KindRequestRejected:   {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
-	KindRequestCompleted:  {audience: AudienceRequester, group: EmailSummary, defaults: allOn},
-	KindRequestPending:    {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
-	KindQuarantineFlagged: {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
-	KindScanFailed:        {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: healthAlert},
-	KindTracksMissing:     {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: healthAlert},
-	KindDuplicatesFound:   {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
-	// Each pass reports what it did itself, so the counts add up.
-	KindDuplicatesResolved: {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: inboxOnly},
+	KindRequestApproved:    {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
+	KindRequestRejected:    {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
+	KindRequestCompleted:   {audience: AudienceRequester, group: EmailSummary, defaults: allOn},
+	KindRequestPending:     {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
+	KindQuarantineFlagged:  {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
+	KindScanFailed:         {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
+	KindTracksMissing:      {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
+	KindDuplicatesFound:    {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
+	KindDuplicatesResolved: {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: inboxOnly},
 	KindPlaybackErrors:     {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
 }