v5.0.0

• Migrate from phpseclib 2.x to actively maintained phpseclib 3.x without raising PHP 7.2.
• Add pre-auth host-key pinning with standard OpenSSH SHA-256 and MD5 fingerprints plus raw host-key access.
• Support passphrase-protected private key files and strings.
• Use SFTP for uploads and downloads, and reject remote symlinks during recursive downloads.
• Expose command exit status, success, and timeout state; apply timeouts to connection and authentication.
• Validate connection, command, key, and transfer inputs explicitly.
• Add passing real-OpenSSH integration tests on PHP 7.2 and PHP 8.5 and document the v5 migration.