fix(centralui): single relay toast, paging/skip polish, extra Site Calls tests

src/ScadaLink.CentralUI/Components/Pages/SiteCalls/SiteCallsReport.razor

@@ -201,6 +201,9 @@
            backwards and the response's NextAfter* cursor to step forwards. *@
         <div class="d-flex justify-content-between align-items-center">
             <span class="text-muted small">
+                @* No "of N" total: keyset paging has no cheap total-count, so
+                   the label is intentionally page-number-only. Do not "fix"
+                   this by adding a total — that would require a COUNT(*). *@
                 Page @(_cursorStack.Count + 1) · @_siteCalls.Count rows
             </span>
             <div>