Retained nonempty SearXNG settings can miss defaults required by newer pinned images while bypassing the entrypoint's narrow regeneration checks.
Add an atomic PyYAML-aware migration to all Compose variants. Preserve existing inheritance choices, custom content, secrets, ownership, and mode while inserting only the missing top-level default-inheritance key.
Validated with 39 focused and adjacent tests, compile checks, and fresh and retained pinned-image HTTP 200 gates. Full repository CI remains for the PR.
