Overhaul docs for auto-bootstrap, Local CA, and whoami tutorial ...

- Remove starter.json (no longer needed — gateway auto-bootstraps on first boot)
- Add envoy/envoy.yaml static bootstrap config
- Fix docker-compose.yml to use envoy.yaml instead of starter.json
- Update README: fix quick start flow, add Local CA section, add tutorial link
- Rewrite getting-started.md: auto-bootstrap, Local CA, bring-your-own-CA
- Update envoy-config.md: replace import section with auto-bootstrap explanation
- Add docs/tutorial-whoami-local-https.md: end-to-end local HTTPS with whoami
- Add configs/README.md: clarify configs dir purpose

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>