A heartbeat-registered site that has never sent a full report now has
LastReportReceivedAt = null instead of the year-0001 sentinel. TimestampDisplay
accepts DateTimeOffset? and renders null as a placeholder ('awaiting first
report') rather than a ~2000-year-stale date. Cross-module: HealthMonitoring +
CentralUI.
Establishes a per-module code review workflow under code-reviews/ and
records the 2026-05-16 baseline review (commit 9c60592): 241 findings
across all src/ modules (6 Critical, 46 High, 100 Medium, 89 Low).
This is the clean starting point for remediation work.