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.SiteEventLogging/EventLogQueryService.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Microsoft.Data.Sqlite;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -135,7 +136,16 @@ public class EventLogQueryService : IEventLogQueryService
                 {
                     rows.Add(new EventLogEntry(
                         Id: reader.GetInt64(0),
-                        Timestamp: DateTimeOffset.Parse(reader.GetString(1)),
+                        // Parse with explicit invariant culture and round-trip style
+                        // (SiteEventLogging-021). Stored values are ISO 8601 "o" UTC
+                        // (see SiteEventLogger.LogEventAsync), and the recorder's
+                        // emitted offset is always +00:00; AssumeUniversal +
+                        // AdjustToUniversal guarantees the parsed value is UTC and
+                        // does not depend on the host's CurrentCulture.
+                        Timestamp: DateTimeOffset.Parse(
+                            reader.GetString(1),
+                            CultureInfo.InvariantCulture,
+                            DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal),
                         EventType: reader.GetString(2),
                         Severity: reader.GetString(3),
                         InstanceId: reader.IsDBNull(4) ? null : reader.GetString(4),