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/library/reconcile.go

@@ -9,7 +9,6 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
-	"git.fabledsword.com/bvandeusen/minstrel/internal/notifications"
 	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
 )
 
@@ -129,9 +128,9 @@ func (s *Scanner) reconcileMissing(
 	// this line.
 	s.logger.Warn("library scan: tracks marked missing (files not found)",
 		"count", n, "library_total", len(rows))
-	if n > 0 {
-		notifyAdmins(ctx, notifications.KindTracksMissing, notifications.Payload{Count: n})
-	}
+	// Admins are told after the scan has adopted moves and folded
+	// replacements, about the ones still gone (notifyStillMissing).
+	stats.marked = toMark
 	return nil
 }