feat(monitor): record probe retry attempts in MonitorLog and surface them in summary

Every probe ping/query now accumulates per-attempt timestamps (attemptedAt,
responseReceivedAt), status, and failure cause across retries. The result rides
along in MonitorLog.logBody so the dashboard can render a retry banner, a
collapsible per-attempt list with both timestamps, and an Attempts column for
all probeable monitors — not just synthetic.