#3926 Showcase countByStatus: $match live statuses before the $group

lib/infrastructure/mongo-showcase-repository.ts countByStatus (added in #1412) runs a $group on $status over the whole profile_showcases collection with no $match. It can walk the { status: 1, createdAt: 1 } index instead of touching documents, but it still scans every entry, withdrawn ones included.

Admin-only, and the collection grows at human speed (every row is an admin-reviewed submission), so this won't matter for a long time. If the admin page ever feels slow, put $match: { status: { $in: ["pending", "approved", "rejected"] } } ahead of the $group so the optimizer uses the index more tightly and skips withdrawn documents.