feat(ui): AuditResultsGrid + AuditLogQueryService with keyset paging (#23 M7)

Adds the results grid + query facade for the central Audit Log page
(#23 M7-T3):

* IAuditLogQueryService / AuditLogQueryService — CentralUI facade over
  IAuditLogRepository.QueryAsync so the grid can be tested with a stubbed
  query source. Default page size is 100; callers can override per call.

* AuditResultsGrid.razor + .razor.cs — Blazor Server component (Bootstrap
  only, no third-party UI libs). Renders the 10 columns from
  Component-AuditLog.md §10 (OccurredAtUtc, Site, Channel, Kind, Status,
  Target, Actor, DurationMs, HttpStatus, ErrorMessage). Keyset-paged via
  the last visible row's (OccurredAtUtc, EventId) as the cursor; Next-page
  button disabled when the current page is short (no count query). Row
  clicks emit OnRowSelected(AuditEvent) for Bundle C's drilldown drawer.
  Status badges are colour-coded (Delivered=green; Failed/Parked/Discarded
  =red; other=gray). Error messages truncated to 80 chars with full text
  on hover.

* Column model framework: a ColumnOrder [Parameter] reorders columns by
  stable string keys; unknown keys are dropped. M7 scope decision (in the
  class doc): the framework is in place but drag-reorder / resize UX is
  not implemented — M7.x can add persisted-per-user reordering without
  rewriting the column model.

* AuditLogPage wired: hosts AuditFilterBar + AuditResultsGrid, threads
  the filter through and stubs OnRowSelected for Bundle C.

* AuditLogQueryService registered as scoped in AddCentralUI.

* Tests: 4 grid bUnit tests (10 columns rendered, next-page cursor
  carries last row, row click raises callback, badge classes for
  Failed vs Delivered), 2 service tests (filter+paging pass-through,
  default page size of 100). AuditLogPageScaffoldTests updated to
  provide the new ISiteRepository + IAuditLogQueryService stubs the
  page now resolves.

tests/ScadaLink.CentralUI.Tests/Services/AuditLogQueryServiceTests.cs

@@ -0,0 +1,57 @@
+using NSubstitute;
+using ScadaLink.CentralUI.Services;
+using ScadaLink.Commons.Entities.Audit;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Types.Audit;
+using ScadaLink.Commons.Types.Enums;
+
+namespace ScadaLink.CentralUI.Tests.Services;
+
+/// <summary>
+/// Service-level tests for <see cref="AuditLogQueryService"/> (#23 M7-T3). The
+/// service is a thin pass-through over <see cref="IAuditLogRepository.QueryAsync"/>;
+/// these tests pin the filter forwarding contract and the 100-row default-page-size
+/// rule the grid relies on.
+/// </summary>
+public class AuditLogQueryServiceTests
+{
+    [Fact]
+    public async Task QueryAsync_ForwardsFilterAndPaging_ToRepository()
+    {
+        var repo = Substitute.For<IAuditLogRepository>();
+        var filter = new AuditLogQueryFilter(Channel: AuditChannel.ApiOutbound);
+        var paging = new AuditLogPaging(PageSize: 25);
+        var expected = new List<AuditEvent>
+        {
+            new() { EventId = Guid.NewGuid(), OccurredAtUtc = DateTime.UtcNow, Channel = AuditChannel.ApiOutbound, Kind = AuditKind.ApiCall, Status = AuditStatus.Delivered }
+        };
+        repo.QueryAsync(filter, paging, Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<AuditEvent>>(expected));
+
+        var sut = new AuditLogQueryService(repo);
+
+        var result = await sut.QueryAsync(filter, paging);
+
+        Assert.Same(expected, result);
+        await repo.Received(1).QueryAsync(filter, paging, Arg.Any<CancellationToken>());
+    }
+
+    [Fact]
+    public async Task QueryAsync_AppliesDefaultPageSize_WhenNotSpecified()
+    {
+        var repo = Substitute.For<IAuditLogRepository>();
+        AuditLogPaging? observed = null;
+        repo.QueryAsync(Arg.Any<AuditLogQueryFilter>(), Arg.Do<AuditLogPaging>(p => observed = p), Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<AuditEvent>>(Array.Empty<AuditEvent>()));
+
+        var sut = new AuditLogQueryService(repo);
+
+        await sut.QueryAsync(new AuditLogQueryFilter(), paging: null);
+
+        Assert.NotNull(observed);
+        Assert.Equal(sut.DefaultPageSize, observed!.PageSize);
+        Assert.Equal(100, sut.DefaultPageSize);
+        Assert.Null(observed.AfterOccurredAtUtc);
+        Assert.Null(observed.AfterEventId);
+    }
+}