feat(ui): scaffold Audit Log page + Audit nav group (#23 M7)

Adds the central-side Audit Log page scaffold at /audit/log (M7-T1) and
introduces a new Audit nav group (M7-T9) that hosts both the new page and
the renamed Configuration Audit Log. The page body is intentionally a
heading + two placeholders — Bundle B will land the AuditFilterBar and
AuditResultsGrid behind them.

The Audit nav group sits between Monitoring and the per-user footer; both
items inside are Admin-only, so the section header lives inside the
RequireAdmin AuthorizeView (non-admins see no orphan header).

bUnit scaffold tests pin the page heading, the section header order, and
the two child links; the existing 338 CentralUI tests continue to pass.

src/ScadaLink.CentralUI/Components/Layout/NavMenu.razor

@@ -108,9 +108,16 @@
                         </Authorized>
                     </AuthorizeView>
 
-                    @* Configuration Audit Log — Admin only *@
+                    @* Audit — Admin only. Hosts the new Audit Log page (#23 M7)
+                       and the renamed Configuration Audit Log (IAuditService
+                       config-change viewer). Both items are Admin-gated, so
+                       the section header sits inside the same policy block. *@
                     <AuthorizeView Policy="@AuthorizationPolicies.RequireAdmin">
                         <Authorized Context="auditContext">
+                            <div role="presentation" class="nav-section-header">Audit</div>
+                            <li class="nav-item">
+                                <NavLink class="nav-link" href="/audit/log">Audit Log</NavLink>
+                            </li>
                             <li class="nav-item">
                                 <NavLink class="nav-link" href="/audit/configuration">Configuration Audit Log</NavLink>
                             </li>

src/ScadaLink.CentralUI/Components/Pages/Audit/AuditLogPage.razor

@@ -0,0 +1,16 @@
+@page "/audit/log"
+@attribute [Authorize]
+
+<PageTitle>Audit Log</PageTitle>
+
+<div class="container-fluid mt-3">
+    <h1 class="h4 mb-3">Audit Log</h1>
+
+    @* AuditFilterBar will go here (Bundle B). *@
+    <div class="mb-3">
+    </div>
+
+    @* AuditResultsGrid will go here (Bundle B). *@
+    <div>
+    </div>
+</div>

src/ScadaLink.CentralUI/Components/Pages/Audit/AuditLogPage.razor.cs

@@ -0,0 +1,12 @@
+namespace ScadaLink.CentralUI.Components.Pages.Audit;
+
+/// <summary>
+/// Code-behind for the central Audit Log page (#23 M7-T1). The Bundle A
+/// scaffold has no behaviour — the filter bar and results grid arrive in
+/// Bundle B (M7-T2..M7-T7). Keeping the partial class in place now lets
+/// later bundles add injected services and event handlers without
+/// touching the route or page-title markup.
+/// </summary>
+public partial class AuditLogPage
+{
+}