Release v2.0.0: Integrate adt-cli core

Major changes:
- Integrated adt-cli core library for security features
- Path traversal protection (validate_path_safe)
- SSRF protection (is_safe_download_url, is_public_ip)
- Strict domain validation (_is_yandex_domain)
- Unified config system with CLI
- Extended DownloadManager with media/cloud/sync support
- Modern UI with status bar and keyboard shortcuts
- Comprehensive documentation (README.md, TECHNICAL.md)