fix(security): close auth & site-scoping gaps across 8 findings

Resolves the auth-theme batch from the 2026-05-28 baseline review (8 findings
across Security/CentralUI/ManagementService/CLI). The most consequential gaps:
NotificationReport + SiteCallsReport now route through SiteScopeService so a
site-scoped Deployment user cannot see or act on other sites' rows (CUI-028);
QueryAuditLogCommand is no longer "any authenticated user" — gated Admin-only
to match /api/audit/query's strictness (MS-018); RoleMapper preserves the
broader grant when a user is in both an unscoped and scoped Deployment LDAP
group, instead of silently narrowing to the scoped set (Sec-016); and the
dead SiteScopeRequirement/Handler are deleted so SiteScopeService is
unambiguously the sole site-scoping mechanism (Sec-017). Pending findings:
172 → 164.

tests/ScadaLink.ManagementService.Tests/AuditEndpointsTests.cs

@@ -530,4 +530,81 @@ public class AuditEndpointsTests
         Assert.Null(paging.AfterEventId);
         Assert.Null(paging.AfterOccurredAtUtc);
     }
+
+    // ─────────────────────────────────────────────────────────────────────
+    // ApplySiteScope (Management-019)
+    // ─────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public void ApplySiteScope_SystemWideUser_ReturnsFilterUnchanged()
+    {
+        // Empty PermittedSiteIds is the system-wide signal (Admin, system-wide
+        // Deployment, audit roles with no scope rules attached). The filter
+        // should pass through with no restriction added.
+        var user = new ScadaLink.Commons.Messages.Management.AuthenticatedUser(
+            "alice", "Alice", new[] { "Admin" }, Array.Empty<string>());
+        var filter = new AuditLogQueryFilter(SourceSiteIds: new[] { "plant-a" });
+
+        var result = AuditEndpoints.ApplySiteScope(filter, user);
+
+        Assert.NotNull(result);
+        Assert.Same(filter, result);
+    }
+
+    [Fact]
+    public void ApplySiteScope_ScopedUser_EmptyCallerFilter_RestrictedToPermittedSet()
+    {
+        // No explicit sourceSiteId from the caller — the helper must restrict
+        // the query to the user's permitted set, otherwise a site-scoped audit
+        // user could read every site's rows.
+        var user = new ScadaLink.Commons.Messages.Management.AuthenticatedUser(
+            "alice", "Alice", new[] { "AuditReadOnly" }, new[] { "plant-a", "plant-b" });
+        var filter = new AuditLogQueryFilter();
+
+        var result = AuditEndpoints.ApplySiteScope(filter, user);
+
+        Assert.NotNull(result);
+        Assert.NotNull(result!.SourceSiteIds);
+        Assert.Equal(new[] { "plant-a", "plant-b" }, result.SourceSiteIds!.OrderBy(s => s).ToArray());
+    }
+
+    [Fact]
+    public void ApplySiteScope_ScopedUser_ExplicitInScopeFilter_KeptVerbatim()
+    {
+        var user = new ScadaLink.Commons.Messages.Management.AuthenticatedUser(
+            "alice", "Alice", new[] { "AuditReadOnly" }, new[] { "plant-a", "plant-b" });
+        var filter = new AuditLogQueryFilter(SourceSiteIds: new[] { "plant-a" });
+
+        var result = AuditEndpoints.ApplySiteScope(filter, user);
+
+        Assert.NotNull(result);
+        Assert.Equal(new[] { "plant-a" }, result!.SourceSiteIds);
+    }
+
+    [Fact]
+    public void ApplySiteScope_ScopedUser_ExplicitOutOfScopeFilter_ReturnsNull()
+    {
+        // Caller explicitly asked for a site they cannot see — the helper signals
+        // "403" by returning null rather than silently producing an empty page.
+        var user = new ScadaLink.Commons.Messages.Management.AuthenticatedUser(
+            "alice", "Alice", new[] { "AuditReadOnly" }, new[] { "plant-a" });
+        var filter = new AuditLogQueryFilter(SourceSiteIds: new[] { "plant-b" });
+
+        var result = AuditEndpoints.ApplySiteScope(filter, user);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void ApplySiteScope_ScopedUser_MixedInAndOutOfScopeFilter_IntersectedToInScopeOnly()
+    {
+        var user = new ScadaLink.Commons.Messages.Management.AuthenticatedUser(
+            "alice", "Alice", new[] { "AuditReadOnly" }, new[] { "plant-a" });
+        var filter = new AuditLogQueryFilter(SourceSiteIds: new[] { "plant-a", "plant-b" });
+
+        var result = AuditEndpoints.ApplySiteScope(filter, user);
+
+        Assert.NotNull(result);
+        Assert.Equal(new[] { "plant-a" }, result!.SourceSiteIds);
+    }
 }