fix(utc/locale): close Theme 2 — 8 UTC / time / locale findings

UTC invariant + culture-safety fixes across UI form binding, audit entity
hydrate, and locale-dependent parses. Highlights:
- CentralUI-026/027: AuditFilterBar / SiteCallsReport / NotificationReport /
  EventLogs now apply SpecifyKind(Local) + ToUniversalTime() at form submit
  so browser-local datetime-local inputs aren't silently treated as UTC.
- Commons-019: AuditEvent.OccurredAtUtc / IngestedAtUtc init-setters
  re-tag any incoming DateTime as Kind=Utc, documenting the invariant.
- CD-018: AuditLogEntityTypeConfiguration adds UTC ValueConverters on the
  *Utc DateTime columns so EF hydrate yields Kind=Utc (SQL Server's
  datetime2 has no Kind metadata, so reads were returning Unspecified).
- CD-020: GetPartitionBoundariesOlderThanAsync now SpecifyKind(Utc) on the
  raw-ADO read, matching the existing defence in AuditLogPartitionMaintenance.
- SEL-021: EventLogQueryService.DateTimeOffset.Parse now uses
  InvariantCulture + AssumeUniversal | AdjustToUniversal.
- SR-023: Convert.ToDouble in ScriptActor + AlarmActor (4 sites) now
  passes InvariantCulture so non-US locales don't mis-parse string values.
- HM-020: CentralHealthAggregator.MarkHeartbeat anchors LastHeartbeatAt to
  max(receivedAt, now) on offline→online so a stale receivedAt can't
  leave a recovered site one tick from re-going-offline.

3 new tests added (AuditLog UTC converter, AuditFilterBar/EventLogs/
NotificationReport-touching CentralUI tests already cover Apply paths,
heartbeat offline→online). Build clean; ConfigurationDatabase 236,
Commons 330, HealthMonitoring 71, SiteRuntime 301, SiteEventLogging 50,
CentralUI 50 — all green. README regenerated: 104 open (was 112).

src/ScadaLink.ConfigurationDatabase/Repositories/AuditLogRepository.cs

@@ -383,7 +383,14 @@ VALUES
             await using var reader = await cmd.ExecuteReaderAsync(ct).ConfigureAwait(false);
             while (await reader.ReadAsync(ct).ConfigureAwait(false))
             {
-                results.Add(reader.GetDateTime(0));
+                // SQL Server's datetime2 surfaces as DateTimeKind.Unspecified
+                // through ADO.NET (the column type carries no offset/kind).
+                // Boundary values are stored in UTC, so re-tag the kind here —
+                // matches the explicit defence in
+                // AuditLogPartitionMaintenance.GetMaxBoundaryAsync and prevents
+                // downstream .ToLocalTime()/.ToUniversalTime() conversions
+                // from silently treating the value as local time.
+                results.Add(DateTime.SpecifyKind(reader.GetDateTime(0), DateTimeKind.Utc));
             }
         }
         finally