Improve documentation and add a setup script for easy deployment on Linux systems.
- Update README.md with instructions for the new multi-voice slash commands and the oices/ directory structure.
- Add a comprehensive 'Linux Server Deployment' section to the README, detailing both a quick setup via a new script and a manual systemd service setup.
- Create setup_linux.sh to automate dependency checking, virtual environment creation, and service installation on Linux.
- Revise comments in .env.example for clarity and to reflect the latest configuration options.
