M19: HTTP middleware records every API call to the immutable audit trail
with method, path, actor, SHA-256 body hash, status, and latency. Best-effort
async recording via goroutine. Health/ready probes excluded.
M16a: Four pluggable notifier connectors — Slack (incoming webhook), Teams
(MessageCard), PagerDuty (Events API v2), OpsGenie (Alert API v2). Each
enabled by config env var. 30 new tests across middleware and connectors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
shankar0123