feat(centralui): Site Call KPI tiles on the Health dashboard

src/ScadaLink.CentralUI/Components/Pages/Monitoring/Health.razor

@@ -8,6 +8,7 @@
 @using ScadaLink.Commons.Interfaces.Repositories
 @using ScadaLink.HealthMonitoring
 @using ScadaLink.Commons.Messages.Notification
+@using ScadaLink.Commons.Messages.Audit
 @using ScadaLink.Communication
 @implements IDisposable
 @inject ICentralHealthAggregator HealthAggregator
@@ -60,6 +61,12 @@
         <div class="text-muted small mb-3">Notification Outbox KPIs unavailable: @_outboxKpiError</div>
     }
 
+    @* Site Call Audit (#22) Task 7 — three KPI tiles for the Site Call channel
+       (buffered / stuck / parked). Refreshed alongside the site states. *@
+    <SiteCallKpiTiles Snapshot="@_siteCallKpi"
+                      IsAvailable="@_siteCallKpiAvailable"
+                      ErrorMessage="@_siteCallKpiError" />
+
     @* Audit Log (#23) M7 Bundle E — three KPI tiles for the Audit channel
        (volume / error rate / backlog). Refreshed alongside the site states. *@
     <AuditKpiTiles Snapshot="@_auditKpi"
@@ -364,6 +371,13 @@
     private bool _auditKpiAvailable;
     private string? _auditKpiError;
 
+    // Site Call Audit (#22) Task 7 — Site Call KPI tiles. Point-in-time counts
+    // from the central SiteCalls table, fetched alongside the site states. The
+    // SiteCallKpiResponse message doubles as the snapshot the tile takes.
+    private SiteCallKpiResponse? _siteCallKpi;
+    private bool _siteCallKpiAvailable;
+    private string? _siteCallKpiError;
+
     private static bool SiteHasActiveErrors(SiteHealthState state)
     {
         var report = state.LatestReport;
@@ -401,6 +415,7 @@
     {
         _siteStates = HealthAggregator.GetAllSiteStates();
         await LoadOutboxKpis();
+        await LoadSiteCallKpis();
         await LoadAuditKpis();
     }
 
@@ -429,6 +444,36 @@
         }
     }
 
+    // Site Call KPI loader: wraps the service call so a transient fault degrades
+    // the three Site Call tiles to em dashes with an inline error rather than
+    // killing the dashboard. Mirrors LoadOutboxKpis's error handling shape — a
+    // response with Success == false (repository fault) and an Ask that threw
+    // (transport fault) both collapse to "unavailable".
+    private async Task LoadSiteCallKpis()
+    {
+        try
+        {
+            var response = await CommunicationService.GetSiteCallKpisAsync(
+                new SiteCallKpiRequest(Guid.NewGuid().ToString("N")));
+            if (response.Success)
+            {
+                _siteCallKpi = response;
+                _siteCallKpiAvailable = true;
+                _siteCallKpiError = null;
+            }
+            else
+            {
+                _siteCallKpiAvailable = false;
+                _siteCallKpiError = response.ErrorMessage ?? "KPI query failed.";
+            }
+        }
+        catch (Exception ex)
+        {
+            _siteCallKpiAvailable = false;
+            _siteCallKpiError = $"KPI query failed: {ex.Message}";
+        }
+    }
+
     // Tiles show the numeric KPI when available, or an em dash when the outbox
     // KPI query failed — matching how the page renders other unavailable data.
     private string OutboxTileValue(int value) =>