Verify the tenant audit-log hash chain

API key required. Walks the caller’s tenant chain from its head, recomputing every visited receipt’s HMAC, and reports whether the chain is intact. Stops at legacy (pre-chain) receipts and reports them as legacyCount. limit bounds how many receipts are checked (default 200, max 1000), newest first. This is the endpoint behind ./writ verify-chain. See the Audit log page for what the chain proves (NIST SP 800-53 AU-9 support).