Verify activity log integrity

Re-reads every event behind the integrity chain and recomputes it, to prove the activity log has not been altered since a digest was recorded. Returns HTTP 200 with ok: false when verification fails, rather than an error status, so a monitoring script can distinguish "the log was altered" from "the check itself failed". This is rate-limited because it re-reads the full log.

Notes.

• Answers 200 with ok: false when verification fails.