Clarify GHCR and runner ownership

[cbusillo]

Summary

• document GHCR retention as repo-local package hygiene
• document runner health as image-build lane telemetry, not Launchplane runtime authority

Tests

• docker run --rm -v "/Users/cbusillo/Developer/odoo-docker:/repo" -w /repo rhysd/actionlint:1.7.12 -config-file .github/actionlint.yaml
• git diff --check