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.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor.cs

@@ -448,11 +448,16 @@ public partial class SiteCallsReport
     private static string? NullIfEmpty(string s) => string.IsNullOrWhiteSpace(s) ? null : s.Trim();
 
     /// <summary>
-    /// The filter inputs are UTC wall-clock — stamp <see cref="DateTimeKind.Utc"/>
-    /// on the local-typed value so the query is unambiguous.
+    /// CentralUI-027: <c>&lt;input type="datetime-local"&gt;</c> binds with
+    /// <see cref="DateTimeKind.Unspecified"/> and the value is the operator's
+    /// browser-local wall-clock. Tag it <see cref="DateTimeKind.Local"/> and
+    /// convert to UTC before the value enters the wire query — otherwise the
+    /// From/To window is silently shifted by the operator's UTC offset.
     /// </summary>
     private static DateTime? ToUtc(DateTime? value) =>
-        value == null ? null : DateTime.SpecifyKind(value.Value, DateTimeKind.Utc);
+        value.HasValue
+            ? DateTime.SpecifyKind(value.Value, DateTimeKind.Local).ToUniversalTime()
+            : (DateTime?)null;
 
     /// <summary>
     /// The <c>SiteCalls</c> timestamps are UTC <see cref="DateTime"/>; wrap them as