Also log staff cancellations via PUT /api/registrations/:id

Registrations can be cancelled two ways: DELETE /:id (owner or admin,
already logged registration_cancelled) and PUT /:id (staff+, status
change endpoint) — the latter was silently unlogged. Since PUT /:id
is staff-only, any transition into 'cancelled' there is inherently a
staff-initiated cancellation, so it's now logged the same way.

Audited all six categories promised in the 1.10.0 changelog entry
(refunds, donation assign/unassign, manual registrations,
staff-initiated cancellations, event create/update/delete, settings
changes) against their actual logAdminAction call sites and route
wiring — this was the only other gap found.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSWFWQsjTc9GyffPiXEDQT

backend/src/controllers/registrationController.js

@@ -626,6 +626,22 @@ const updateRegistrationStatus = async (req, res) => {
       }
     });
 
+    // This is the staff-only status-change endpoint (separate from the owner-facing
+    // DELETE /:id cancel route), so any transition into 'cancelled' here is always a
+    // staff-initiated cancellation — log it the same way DELETE /:id does, so both
+    // paths land under the one 'registration_cancelled' filter in the audit log.
+    if (status === 'cancelled' && registration.status !== 'cancelled') {
+      logAdminAction({
+        actorId: req.user.id,
+        actorRole: req.user.role,
+        action: 'registration_cancelled',
+        targetType: 'Registration',
+        targetId: req.params.id,
+        metadata: { registrationOwnerId: registration.userId, previousStatus: registration.status },
+        ip: getClientIp(req),
+      });
+    }
+
     // Generate tickets and email them when status is manually set to 'paid' by staff
     if (status === 'paid') {
       (async () => {