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/db/dbq/notifications.sql.go

@@ -346,8 +346,9 @@ type MarkAllNotificationsReadParams struct {
 
 // up_to, when set, limits it to what existed when the user asked: a "mark
 // all read" queued offline and replayed later must not mark notices that
-// arrived in between, which the user never saw. A coalesced row updated
-// since then carries a newer created_at, so it stays unread too.
+// arrived in between, which the user never saw. A coalesced row that grew
+// since then is marked read with it: it arrived before they asked, and its
+// growth is a quiet update to a notice they had seen (M542).
 func (q *Queries) MarkAllNotificationsRead(ctx context.Context, arg MarkAllNotificationsReadParams) (int64, error) {
 	result, err := q.db.Exec(ctx, markAllNotificationsRead, arg.UserID, arg.UpTo)
 	if err != nil {
@@ -457,15 +458,15 @@ VALUES ($1, $2, $3, $4,
         CASE WHEN $5::boolean THEN NULL ELSE now() END)
 ON CONFLICT (user_id, coalesce_key) WHERE read_at IS NULL AND coalesce_key IS NOT NULL
 DO UPDATE SET
-    payload = CASE
-        WHEN $6::boolean THEN
-            EXCLUDED.payload || jsonb_build_object('count',
-                COALESCE((user_notifications.payload->>'count')::bigint, 0)
-              + COALESCE((EXCLUDED.payload->>'count')::bigint, 0))
-        ELSE EXCLUDED.payload
-    END,
-    created_at = now(),
-    emailed_at = EXCLUDED.emailed_at
+    payload = EXCLUDED.payload || jsonb_build_object(
+        'count', COALESCE((user_notifications.payload->>'count')::bigint, 0)
+               + COALESCE((EXCLUDED.payload->>'count')::bigint, 0),
+        'items', (SELECT COALESCE(jsonb_agg(e.item ORDER BY e.n), '[]'::jsonb)
+                    FROM jsonb_array_elements(
+                             COALESCE(EXCLUDED.payload->'items', '[]'::jsonb)
+                          || COALESCE(user_notifications.payload->'items', '[]'::jsonb)
+                         ) WITH ORDINALITY AS e(item, n)
+                   WHERE e.n <= 10))
 RETURNING id
 `
 
@@ -475,20 +476,18 @@ type UpsertCoalescedNotificationParams struct {
 	Payload     []byte
 	CoalesceKey *string
 	EmailWanted bool
-	SumCount    bool
 }
 
 // One unread row per (user, coalesce_key). A new event while that row is
-// unread updates it in place and moves it back to the top of the inbox.
+// unread updates it in place: its `count` adds to the row's, and its `items`
+// (the names of what changed) go in front of the row's, keeping the newest
+// ten. Every coalesced kind's event is "N more happened", never a restated
+// total, so the row always says what is new since it was last read.
 //
-// sum_count: the payload's `count` adds to the unread row's count rather than
-// replacing it. For kinds whose event is "N more happened" (tracks marked
-// missing). Kinds whose event states the whole current total (pending
-// duplicate groups) pass false and the payload simply replaces.
-//
-// emailed_at is cleared so the newer state goes out in the next batch; an
-// emailed-but-unread row that keeps growing is news the user hasn't seen.
-// Unless email_wanted is false, as in InsertNotification.
+// created_at and emailed_at are left alone (M542): an update changes what the
+// notice says, not when it arrived. Moving created_at made the phone announce
+// it again and clearing emailed_at sent it again, so a notice the hourly
+// duplicate pass kept growing alerted every hour.
 func (q *Queries) UpsertCoalescedNotification(ctx context.Context, arg UpsertCoalescedNotificationParams) (pgtype.UUID, error) {
 	row := q.db.QueryRow(ctx, upsertCoalescedNotification,
 		arg.UserID,
@@ -496,7 +495,6 @@ func (q *Queries) UpsertCoalescedNotification(ctx context.Context, arg UpsertCoa
 		arg.Payload,
 		arg.CoalesceKey,
 		arg.EmailWanted,
-		arg.SumCount,
 	)
 	var id pgtype.UUID
 	err := row.Scan(&id)