- rootfs: create readonly global `rootfs_cache_id` (type+hash+date/version)
- add "oras-upload" CLI command (dumb, no retries, single target/single source)
- docker: mount-bind for & re-pass envs `GITHUB_OUTPUT` and `GITHUB_STEP_SUMMARY` down to Docker
- introduce `github-actions.sh::github_actions_add_output()`
- during logs cleanup, dump the Markdown log into GITHUB_STEP_SUMMARY if it is available
