dsh-vps: Running DeepSeek Harness on Your VPS

The `dsh-vps` plugin solves the issue that DeepSeek Harness trusts local browsers only by default by placing a zero-runtime-dependency `dsh-gate` login gateway in front of it. It supports dual deployment modes (DSH plugin or one-click script), uses scrypt-based login with secure cookie mechanisms, and leverages Caddy to enable public internet access. Features include bilingual support, automatic HTTPS, session persistence, and one-click upgrade/rollback. This solution preserves the full DSH native interface while enabling a secure and convenient public-facing private deployment.