feat(centralui): column resize and reorder for the audit results grid

Adds drag-to-resize and drag-to-reorder column UX to AuditResultsGrid,
with chosen widths + column order persisted in browser sessionStorage.

- wwwroot/js/audit-grid.js: dependency-free helper — pointer-driven
  resize handles, native HTML5 drag-and-drop reorder, and a
  sessionStorage save/load wrapper (mirrors treeview-storage.js).
- AuditResultsGrid: renders a resize handle per <th>, makes headers
  draggable, applies persisted widths via a --audit-col-width custom
  property, and wires reorder into the existing ColumnOrder /
  OrderedColumns() mechanism. JS-invokable OnColumnResized /
  OnColumnReordered persist + re-render. A stored order naming an
  unknown column degrades gracefully (drops unknown keys, appends
  missing columns in default order); widths clamp to a 64px minimum.
- AuditResultsGrid.razor.css: subtle scoped styling for the resize
  handle affordance and the reorder drop-target highlight.
- App.razor references audit-grid.js alongside the other scripts.
- Tests: 6 new bUnit tests for the load/apply/persist logic and
  graceful degradation; a new AuditGridColumnTests Playwright suite
  for the drag UX + reload persistence. Audit page bUnit tests set
  loose JSInterop mode since the grid now calls into audit-grid.js.

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

@@ -12,12 +12,20 @@
     }
 
     <div class="table-responsive">
-        <table class="table table-sm table-hover align-middle">
+        <table class="table table-sm table-hover align-middle" @ref="_tableRef">
             <thead class="table-light">
                 <tr>
                     @foreach (var col in OrderedColumns())
                     {
-                        <th data-test="col-header-@col.Key">@col.Label</th>
+                        <th class="audit-grid-th"
+                            data-test="col-header-@col.Key"
+                            data-col-key="@col.Key"
+                            style="@ColumnWidthStyle(col.Key)">
+                            @col.Label
+                            <span class="audit-grid-resize-handle"
+                                  data-test="col-resize-@col.Key"
+                                  aria-hidden="true"></span>
+                        </th>
                     }
                 </tr>
             </thead>
@@ -48,7 +56,7 @@
                             @onclick="() => HandleRowClick(row)">
                             @foreach (var col in OrderedColumns())
                             {
-                                <td>
+                                <td class="audit-grid-td" style="@ColumnWidthStyle(col.Key)">
                                     @RenderCell(col.Key, row)
                                 </td>
                             }