feat(theme): NavRailSection data-nav-key for persistence

ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/Components/NavRailSection.razor

@@ -1,7 +1,7 @@
 @* Components/NavRailSection.razor — CSS-only collapsible (no JS, works in static SSR).
    Apps that want cookie-persisted expand state keep their own interactive NavSection. *@
 @namespace ZB.MOM.WW.Theme
-<details class="rail-section" open="@Expanded">
+<details class="rail-section" open="@Expanded" data-nav-key="@ResolvedKey">
     <summary class="rail-eyebrow-toggle">@Title</summary>
     <div class="rail-section-body">@ChildContent</div>
 </details>
@@ -18,8 +18,23 @@
     /// </summary>
     [Parameter] public bool Expanded { get; set; } = true;
 
+    /// <summary>
+    /// Stable identifier used to persist this section's open/closed state in
+    /// localStorage (via the kit's nav-state.js). Defaults to a slug of <see cref="Title"/>.
+    /// </summary>
+    [Parameter] public string? Key { get; set; }
+
     /// <summary>
     /// Section content — typically <see cref="NavRailItem"/> children.
     /// </summary>
     [Parameter] public RenderFragment? ChildContent { get; set; }
+
+    private string ResolvedKey => string.IsNullOrWhiteSpace(Key) ? Slug(Title) : Key!;
+
+    private static string Slug(string s)
+    {
+        var chars = s.Trim().ToLowerInvariant()
+            .Select(c => char.IsLetterOrDigit(c) ? c : '-').ToArray();
+        return string.Join('-', new string(chars).Split('-', StringSplitOptions.RemoveEmptyEntries));
+    }
 }