feat(sitecallaudit): query, KPI and detail backend for the Site Calls page

src/ScadaLink.Commons/Types/Audit/SiteCallKpiSnapshot.cs

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+namespace ScadaLink.Commons.Types.Audit;
+
+/// <summary>
+/// Point-in-time operational metrics for the central <c>SiteCalls</c> table
+/// (Site Call Audit #22), surfaced on the health dashboard. The cached-call
+/// counterpart of <see cref="ScadaLink.Commons.Types.Notifications.NotificationKpiSnapshot"/>;
+/// mirrors its shape so the Central UI Site Calls KPI tiles can reuse the
+/// Notification Outbox tile layout.
+/// </summary>
+/// <param name="BufferedCount">
+/// Count of non-terminal rows (<c>Pending</c> + <c>Retrying</c>) — calls
+/// buffered at sites awaiting retry.
+/// </param>
+/// <param name="ParkedCount">Count of rows in the <c>Parked</c> status.</param>
+/// <param name="FailedLastInterval">
+/// Count of <c>Failed</c> rows whose <see cref="ScadaLink.Commons.Entities.Audit.SiteCall.TerminalAtUtc"/>
+/// is at or after the supplied "since" timestamp.
+/// </param>
+/// <param name="DeliveredLastInterval">
+/// Count of <c>Delivered</c> rows whose <see cref="ScadaLink.Commons.Entities.Audit.SiteCall.TerminalAtUtc"/>
+/// is at or after the supplied "since" timestamp.
+/// </param>
+/// <param name="OldestPendingAge">
+/// Age of the oldest non-terminal row (<c>now - min(CreatedAtUtc)</c>), or
+/// <c>null</c> when there are no non-terminal rows.
+/// </param>
+/// <param name="StuckCount">
+/// Count of non-terminal rows (<c>Pending</c>/<c>Retrying</c>) whose
+/// <see cref="ScadaLink.Commons.Entities.Audit.SiteCall.CreatedAtUtc"/> is older
+/// than the supplied stuck cutoff. Display-only — no escalation.
+/// </param>
+public sealed record SiteCallKpiSnapshot(
+    int BufferedCount,
+    int ParkedCount,
+    int FailedLastInterval,
+    int DeliveredLastInterval,
+    TimeSpan? OldestPendingAge,
+    int StuckCount);

src/ScadaLink.Commons/Types/Audit/SiteCallSiteKpiSnapshot.cs

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+namespace ScadaLink.Commons.Types.Audit;
+
+/// <summary>
+/// Point-in-time <c>SiteCalls</c> metrics scoped to a single source site. The
+/// per-site counterpart of <see cref="SiteCallKpiSnapshot"/>; surfaced in the
+/// per-site breakdown table on the Site Calls KPIs page. Mirrors
+/// <see cref="ScadaLink.Commons.Types.Notifications.SiteNotificationKpiSnapshot"/>.
+/// </summary>
+/// <param name="SourceSite">The site identifier these metrics are scoped to.</param>
+/// <param name="BufferedCount">Count of this site's non-terminal rows (<c>Pending</c> + <c>Retrying</c>).</param>
+/// <param name="ParkedCount">Count of this site's rows in the <c>Parked</c> status.</param>
+/// <param name="FailedLastInterval">
+/// Count of this site's <c>Failed</c> rows whose <c>TerminalAtUtc</c> is at or
+/// after the "since" timestamp.
+/// </param>
+/// <param name="DeliveredLastInterval">
+/// Count of this site's <c>Delivered</c> rows whose <c>TerminalAtUtc</c> is at
+/// or after the "since" timestamp.
+/// </param>
+/// <param name="OldestPendingAge">
+/// Age of this site's oldest non-terminal row, or <c>null</c> when it has none.
+/// </param>
+/// <param name="StuckCount">
+/// Count of this site's non-terminal rows whose <c>CreatedAtUtc</c> is older
+/// than the stuck cutoff.
+/// </param>
+public sealed record SiteCallSiteKpiSnapshot(
+    string SourceSite,
+    int BufferedCount,
+    int ParkedCount,
+    int FailedLastInterval,
+    int DeliveredLastInterval,
+    TimeSpan? OldestPendingAge,
+    int StuckCount);