feat(waitlist): queue position on the customer manage page

A waitlisted customer saw only a bare status — worse, the badge fell
back to "Pending" for both waitlisted and cancelled states. The view
now carries a 1-based waitlistPosition (earlier-created waitlisted
bookings on the session + 1) and the page renders a warning-tone
notice with the queue spot and auto-promotion explanation, in CS/EN.
Also fixed the badge's nonexistent --danger-soft/--warning-soft tokens.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/db/repository.go

@@ -107,6 +107,7 @@ type Repository interface {
 	// Customer Booking Management
 	GetBookingByReference(ctx context.Context, reference string) (BookingRecord, error)
 	GetBookingByID(ctx context.Context, bookingID string) (BookingRecord, error)
+	GetWaitlistPosition(ctx context.Context, sessionID, bookingID string) (int, error)
 	UpdateBookingStatus(ctx context.Context, bookingID string, status string) error
 	RescheduleBooking(ctx context.Context, bookingID string, startsAt time.Time, endsAt time.Time) error
 
@@ -1844,6 +1845,27 @@ func (r *MemoryRepository) GetBookingByID(_ context.Context, bookingID string) (
 	return BookingRecord{}, pgx.ErrNoRows
 }
 
+func (r *MemoryRepository) GetWaitlistPosition(_ context.Context, sessionID, bookingID string) (int, error) {
+	var self *BookingRecord
+	for index := range r.bookings {
+		if r.bookings[index].ID == bookingID {
+			self = &r.bookings[index]
+			break
+		}
+	}
+	if self == nil {
+		return 0, pgx.ErrNoRows
+	}
+	position := 1
+	for _, booking := range r.bookings {
+		if booking.ClassSessionID != nil && *booking.ClassSessionID == sessionID &&
+			booking.Status == "waitlisted" && booking.CreatedAt.Before(self.CreatedAt) {
+			position++
+		}
+	}
+	return position, nil
+}
+
 func (r *MemoryRepository) UpdateBookingStatus(_ context.Context, bookingID string, status string) error {
 	for i, b := range r.bookings {
 		if b.ID == bookingID {