Implement cross-platform log streaming for frpc instances with support for Windows, systemd, and init.d systems. Includes WebSocket API endpoint for real-time log streaming, token validation, and instance ownership checks. Update README and API documentation to reflect new functionality.
The implementation handles:
- Platform-specific log collection (Windows Event Log, journalctl, log files)
- WebSocket-based real-time streaming
- Token validation and instance access control
- Log level parsing and formatting
- Historical log retrieval since service start
