Redact ticket title for non-public tickets in create/status-change Matrix notifications (#46)

sendTicketNotification() and sendStatusChangeNotification() always sent
the ticket title to the shared MATRIX_NOTIFY_USERS list regardless of
visibility, unlike sendCommentNotification()/notifyWatchers() which
already redact the comment/activity preview for non-public tickets.
Creating or changing the status of a confidential ticket broadcast its
title to a shared Matrix room, defeating the point of the Confidential
visibility level.

Added a shared redactedTitle() helper and threaded visibility through
both functions (sendTicketNotification reads it from the existing
$ticketData['visibility'] key; sendStatusChangeNotification takes a new
optional parameter, wired up in both callers from the already-fetched
ticket row). Verified end-to-end with a local HTTP server capturing the
actual webhook payloads: public tickets pass the title through
unchanged, confidential/internal tickets get the redacted placeholder.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015nCxwFFsy8ouMWzn56rPVP

api/update_ticket.php

@@ -267,7 +267,8 @@ try {
                     $currentTicket['status'],
                     $updateData['status'],
                     $updateData['title'],
-                    $changedBy
+                    $changedBy,
+                    $currentTicket['visibility'] ?? 'public'
                 );
                 NotificationHelper::notifyWatchers(
                     $this->conn,