Updated README to explain new auto-resume behavior:
- API key can be stored in settings.json (no need to export every time)
- Letta auto-resumes the last agent used in each directory
- No need for --continue flag in most cases
- Added --new flag documentation
- Clarified .letta/settings.local.json is gitignored and personal
- Marked --continue as deprecated
👾 Generated with [Letta Code](https://letta.com)
Co-Authored-By: Letta <noreply@letta.com>
