Inventory + implement scriptable checks for preflight-learning-path

## Context

Follow-on from the epic's script-based review work (#579, #581). Preflight currently relies entirely on agent judgment; some of its checks may be mechanical enough to script, same as the review-companion checks.

## Scope

- Extend the script-now / script-later / keep-agent inventory from #579 to cover preflight-specific checks
- Reuse/wire the highest-ROI scripts from #581 into the preflight flow where applicable, so preflight and review share the same scripted checks instead of duplicating logic

## Success criteria

- [ ] Preflight checks classified alongside #579's inventory
- [ ] Preflight reuses scripts from #581 rather than re-implementing equivalent checks

## Priority

Lower priority — sequence after #579/#581 land.

## Related

Part of epic #577. Depends on #579, #581.