Khaos Login / CLI Updates

v1.0.5: promote login/logout to top-level commands

- Extract `khaos login` and `khaos logout` as standalone commands
  (previously `khaos sync --login` / `khaos sync --logout`)
- Add helpful decorator example when `khaos discover` finds no agents
- Update all CLI hints and error messages to reference new commands
- Add deprecation entries for `sync --login` / `sync --logout`
- Bump version to 1.0.5