fix(helpdesk): detect file extension from magic bytes when filename has none

OData TicketLog doesn't expose the original filename (DataText field).
When the derived filename has no extension, detect the file type from
magic bytes (PNG, JPEG, GIF, PDF, ZIP) and append the correct extension.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/helpdesk/pages/helpdesk/ticket-file-data().php

@@ -79,7 +79,19 @@ if (strlen($data) > $maxFileSize) {
     return;
 }
 
+// Ensure filename has an extension — derive from content if missing
 $displayFilename = $filename !== '' ? $filename : 'attachment-' . $entryNo;
+if (!str_contains($displayFilename, '.')) {
+    $ext = match (true) {
+        str_starts_with($data, "\x89PNG") => '.png',
+        str_starts_with($data, "\xFF\xD8\xFF") => '.jpg',
+        str_starts_with($data, "GIF8") => '.gif',
+        str_starts_with($data, "%PDF") => '.pdf',
+        str_starts_with($data, "PK\x03\x04") => '.zip',
+        default => '',
+    };
+    $displayFilename .= $ext;
+}
 
 header('X-Content-Type-Options: nosniff');
 header('Content-Security-Policy: sandbox');