feat(activity): per-tenant audit feed in notification dropdown

activity_events records booking lifecycle transitions with the actor
behind each change — staff (dashboard), customer (self-service), or
system (auto-promotion). The notification dropdown leads with the real
feed instead of derived recent-booking guesses.

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

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

apps/backend/internal/bookings/customer_service.go

@@ -226,6 +226,17 @@ func (s *CustomerService) RescheduleBooking(ctx context.Context, reference strin
 		}
 	}
 
+	serviceName, _ := s.descriptors(ctx, booking)
+	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
+		TenantID:   booking.TenantID,
+		ActorKind:  "customer",
+		ActorName:  booking.CustomerName,
+		Action:     "booking.rescheduled",
+		EntityType: "booking",
+		EntityID:   &booking.ID,
+		Summary:    booking.CustomerName + " — " + serviceName,
+	})
+
 	// Send reschedule email (async)
 	go s.sendRescheduleEmail(booking, newStartsAt, newEndsAt)
 
@@ -250,6 +261,16 @@ func (s *CustomerService) CancelBooking(ctx context.Context, reference string, t
 		return err
 	}
 	_ = s.repo.CancelPendingReminderJobsForBooking(ctx, booking.ID)
+	serviceName, _ := s.descriptors(ctx, booking)
+	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
+		TenantID:   booking.TenantID,
+		ActorKind:  "customer",
+		ActorName:  booking.CustomerName,
+		Action:     "booking.cancelled",
+		EntityType: "booking",
+		EntityID:   &booking.ID,
+		Summary:    booking.CustomerName + " — " + serviceName,
+	})
 
 	// Send cancellation email (async)
 	go s.sendCancellationEmail(booking)
@@ -534,6 +555,15 @@ func (s *CustomerService) MoveBookingToSession(ctx context.Context, reference st
 
 	updated := booking
 	updated.ClassSessionID = &target.ID
+	_ = s.repo.AppendActivityEvent(ctx, db.ActivityEventParams{
+		TenantID:   booking.TenantID,
+		ActorKind:  "customer",
+		ActorName:  booking.CustomerName,
+		Action:     "booking.moved",
+		EntityType: "booking",
+		EntityID:   &booking.ID,
+		Summary:    booking.CustomerName + " — " + target.Title,
+	})
 	go s.sendRescheduleEmail(updated, target.StartsAt, target.EndsAt)
 
 	return domain.MoveBookingResponse{Status: newStatus}, nil