Fixes#600
Three improvements to `--native` Chrome launching:
- `find_chrome()` now falls back to Playwright's browser cache (`~/.cache/ms-playwright/`) when no system Chrome is found
- Auto-detect containers/VMs (root, Docker, Podman, cgroups) and inject `--no-sandbox`
- Chrome stderr is now captured and included in launch error messages, with a hint when sandbox errors are detected