Persists and loads .scoria/install/manifest.json as the last-applied install snapshot.

The manifest is written after a successful apply. load/1 is informational for the planner and report surfaces only — it is not a check-time drift baseline.

validate_freshness/2 runs at apply time: it compares each plan entry's live :fingerprint (captured when the plan was built) to the current disk fingerprint. It does not read the stored manifest file for that gate.