bulk_operation.php: ticket ID validation was converting IDs to int then back
to string, so '000123456' became '123456' which never matched the DB VARCHAR
key, silently rejecting ~11% of tickets from bulk operations. Now validates
with ctype_digit() to preserve leading zeros.
TicketModel::getTicketsByIds(): changed intval() to strval() and bind type
'i' to 's' so VARCHAR ticket_id columns are queried consistently as strings.
DashboardController::getCategoriesAndTypes(): added null check on query
result before calling fetch_assoc() to prevent TypeError if query fails.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>