Fix loose comparisons in authorization checks

- TicketModel.php: fix bind_param "sssi"→"issi" for ticketId in addComment()
- TicketModel.php: use strict (int) cast === for confidential ticket access check
- update_ticket.php: use strict (int) cast !== for creator/assignee auth check
- AttachmentModel.php: use strict (int) cast === for upload ownership check

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

api/update_ticket.php

@@ -92,8 +92,8 @@ try {
 
             // Authorization: admins can edit any ticket; others only their own or assigned
             if (!$this->isAdmin
-                && $currentTicket['created_by'] != $this->userId
-                && $currentTicket['assigned_to'] != $this->userId
+                && (int)$currentTicket['created_by'] !== (int)$this->userId
+                && (int)$currentTicket['assigned_to'] !== (int)$this->userId
             ) {
                 return [
                     'success' => false,