Wire optimistic locking, visibility audit log, full ticket export

Optimistic locking:
- TicketView now includes updated_at in window.ticketData
- ticket.js saveTicket() sends expected_updated_at on every save so
  the server can detect concurrent edits
- On conflict response, shows a clear toast: "ticket was modified by
  someone else while you were editing — reload to see latest version"
- On success, syncs window.ticketData.updated_at from server response
  so subsequent saves use the correct lock key
- update_ticket.php now returns updated_at in success response

Visibility audit log:
- updateVisibility() result is now checked; on success, logs a delta
  entry to the audit trail with from/to visibility and groups so the
  timeline shows who changed visibility and when

Full ticket export:
- export_tickets.php now accepts format=full with a single ticket_id
- Produces a JSON file containing ticket fields, flat comment list
  (with author, timestamps, text), and the full audit timeline
- Access-controlled: respects canUserAccessTicket() before exporting
- EXPORT button added to ticket toolbar linking directly to the endpoint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/update_ticket.php

@@ -177,7 +177,18 @@ try {
                     ];
                 }
 
-                $this->ticketModel->updateVisibility($id, $data['visibility'], $visibilityGroups, $this->userId);
+                $visResult = $this->ticketModel->updateVisibility($id, $data['visibility'], $visibilityGroups, $this->userId);
+                if ($visResult && $this->userId) {
+                    $this->auditLog->log(
+                        $this->userId, 'update', 'ticket', (string)$id,
+                        [
+                            'field'      => 'visibility',
+                            'from'       => $currentTicket['visibility'] ?? 'public',
+                            'to'         => $data['visibility'],
+                            'groups'     => $visibilityGroups
+                        ]
+                    );
+                }
             }
 
             // Log ticket update to audit log — only the changed fields (delta)
@@ -197,10 +208,11 @@ try {
             }
 
             return [
-                'success' => true,
-                'status' => $updateData['status'],
-                'priority' => $updateData['priority'],
-                'message' => 'Ticket updated successfully'
+                'success'    => true,
+                'status'     => $updateData['status'],
+                'priority'   => $updateData['priority'],
+                'updated_at' => date('Y-m-d H:i:s'),
+                'message'    => 'Ticket updated successfully'
             ];
         }
     }