Fix file upload security, bind_param mismatch, and cookie flags

- upload_attachment.php: derive stored file extension from validated MIME type
  instead of user-supplied filename, preventing executable extension attacks
  (e.g. a PHP file renamed to evil.txt would now be stored as .txt)
- CustomFieldModel.php: fix bind_param type string in updateDefinition()
  'sssssiiiii' (10 chars) → 'sssssiiii' (9 chars) to match 9 SQL placeholders
- RateLimitMiddleware.php: replace MD5 with SHA256 for rate limit file hashing
- user_preferences.php: add httponly, secure, samesite=Lax flags to ticketsPerPage
  cookie to prevent XSS/CSRF cookie theft

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

api/upload_attachment.php

@@ -151,10 +151,26 @@ if (!is_dir($ticketDir)) {
     }
 }
 
-// Generate unique filename
-$extension = pathinfo($file['name'], PATHINFO_EXTENSION);
-$safeExtension = preg_replace('/[^a-zA-Z0-9]/', '', $extension);
-$uniqueFilename = uniqid('att_', true) . ($safeExtension ? '.' . $safeExtension : '');
+// Derive extension from validated MIME type (never from user-supplied filename)
+// This prevents executable extension attacks (e.g. evil.php disguised as text/plain)
+$mimeToExt = [
+    'image/jpeg'       => 'jpg',  'image/png'  => 'png',
+    'image/gif'        => 'gif',  'image/webp' => 'webp',
+    'application/pdf'  => 'pdf',
+    'text/plain'       => 'txt',  'text/csv'   => 'csv',
+    'application/msword' => 'doc',
+    'application/vnd.openxmlformats-officedocument.wordprocessingml.document' => 'docx',
+    'application/vnd.ms-excel' => 'xls',
+    'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' => 'xlsx',
+    'application/zip'  => 'zip',
+    'application/x-7z-compressed' => '7z',
+    'application/x-tar' => 'tar',
+    'application/gzip' => 'gz',
+    'application/json' => 'json',
+    'application/xml'  => 'xml',
+];
+$safeExtension = $mimeToExt[$mimeType] ?? 'bin';
+$uniqueFilename = uniqid('att_', true) . '.' . $safeExtension;
 $targetPath = $ticketDir . '/' . $uniqueFilename;
 
 // Move uploaded file

api/user_preferences.php

@@ -43,7 +43,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
                 if (!in_array($key, $validKeys)) continue;
                 $prefsModel->setPreference($userId, $key, $value);
                 if ($key === 'rows_per_page') {
-                    setcookie('ticketsPerPage', $value, time() + (86400 * 365), '/');
+                    setcookie('ticketsPerPage', $value, ['expires' => time() + (86400 * 365), 'path' => '/', 'httponly' => true, 'secure' => true, 'samesite' => 'Lax']);
                 }
             }
             echo json_encode(['success' => true]);