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.

src/ScadaLink.CentralUI/Components/Audit/AuditResultsGrid.razor

@@ -0,0 +1,111 @@
+@using ScadaLink.CentralUI.Components.Shared
+@using ScadaLink.CentralUI.Services
+@using ScadaLink.Commons.Entities.Audit
+@using ScadaLink.Commons.Types.Audit
+@using ScadaLink.Commons.Types.Enums
+@inject IAuditLogQueryService QueryService
+
+<div data-test="audit-results-grid">
+    @if (_error is not null)
+    {
+        <div class="alert alert-danger small mb-2">@_error</div>
+    }
+
+    <div class="table-responsive">
+        <table class="table table-sm table-hover align-middle">
+            <thead class="table-light">
+                <tr>
+                    @foreach (var col in OrderedColumns())
+                    {
+                        <th data-test="col-header-@col.Key">@col.Label</th>
+                    }
+                </tr>
+            </thead>
+            <tbody>
+                @if (_rows.Count == 0)
+                {
+                    <tr>
+                        <td colspan="@OrderedColumns().Count" class="text-muted small text-center py-4">
+                            @if (_loading)
+                            {
+                                <span>Loading…</span>
+                            }
+                            else
+                            {
+                                <span>No audit events match the current filter.</span>
+                            }
+                        </td>
+                    </tr>
+                }
+                else
+                {
+                    @foreach (var row in _rows)
+                    {
+                        <tr @key="row.EventId"
+                            data-test="grid-row-@row.EventId"
+                            class="audit-row"
+                            style="cursor: pointer;"
+                            @onclick="() => HandleRowClick(row)">
+                            @foreach (var col in OrderedColumns())
+                            {
+                                <td>
+                                    @RenderCell(col.Key, row)
+                                </td>
+                            }
+                        </tr>
+                    }
+                }
+            </tbody>
+        </table>
+    </div>
+
+    <div class="d-flex justify-content-between align-items-center">
+        <span class="text-muted small">Page @_pageNumber · @_rows.Count rows</span>
+        <button class="btn btn-outline-secondary btn-sm"
+                data-test="grid-next-page"
+                disabled="@(_loading || _rows.Count < _pageSize)"
+                @onclick="NextPage">Next page</button>
+    </div>
+</div>
+
+@code {
+    private RenderFragment RenderCell(string key, AuditEvent row) => __builder =>
+    {
+        switch (key)
+        {
+            case "OccurredAtUtc":
+                var occurredOffset = new DateTimeOffset(DateTime.SpecifyKind(row.OccurredAtUtc, DateTimeKind.Utc));
+                <span title="@row.OccurredAtUtc.ToString("u")">
+                    <TimestampDisplay Value="occurredOffset" Format="yyyy-MM-dd HH:mm:ss" />
+                </span>
+                break;
+            case "Site":
+                <span class="small">@(row.SourceSiteId ?? "—")</span>
+                break;
+            case "Channel":
+                <span class="small">@row.Channel</span>
+                break;
+            case "Kind":
+                <span class="small">@row.Kind</span>
+                break;
+            case "Status":
+                <span data-test="status-badge-@row.EventId" class="badge @StatusBadgeClass(row.Status)">@row.Status</span>
+                break;
+            case "Target":
+                <span class="small">@(row.Target ?? "—")</span>
+                break;
+            case "Actor":
+                <span class="small">@(row.Actor ?? "—")</span>
+                break;
+            case "DurationMs":
+                <span class="small font-monospace">@(row.DurationMs?.ToString() ?? "—")</span>
+                break;
+            case "HttpStatus":
+                <span class="small font-monospace">@(row.HttpStatus?.ToString() ?? "—")</span>
+                break;
+            case "ErrorMessage":
+                <span class="small text-danger" title="@row.ErrorMessage">@TruncateError(row.ErrorMessage)</span>
+                break;
+        }
+    };
+}