fix(nav): per-parent dropdown collapsed state; reset on focusout

HashSet<string> _collapsedDropdowns replaces single bool so each parent
tracks its own dismiss state independently. onfocusout added alongside
onmouseleave so keyboard users get the dropdown re-enabled without a
mouse pass after Enter-activating a child link.

DeepDrftPublic.Client/Layout/DeepDrftMenu.razor

@@ -17,15 +17,16 @@
                        dd-nav-item-collapsed is added on child click to force-hide the
                        dropdown after SPA navigation (which keeps the DOM and may leave
                        :hover true). It is cleared on mouseleave so the next hover works. *@
-                    <li class="dd-nav-item-parent @(_dropdownCollapsed ? "dd-nav-item-collapsed" : "")"
-                        @onmouseleave="ResetDropdown">
+                    <li class="dd-nav-item-parent @(_collapsedDropdowns.Contains(navPage.Route) ? "dd-nav-item-collapsed" : "")"
+                        @onmouseleave="() => ResetDropdown(navPage.Route)"
+                        @onfocusout="() => ResetDropdown(navPage.Route)">
                         <a href="@navPage.Route" class="dd-nav-link">@navPage.Name</a>
                         <ul class="dd-nav-dropdown">
                             @foreach (var child in navPage.Children)
                             {
                                 <li>
                                     <a href="@child.Route" class="dd-nav-link dd-nav-dropdown-link"
-                                       @onclick="CollapseDropdown">@child.Name</a>
+                                       @onclick="() => CollapseDropdown(navPage.Route)">@child.Name</a>
                                 </li>
                             }
                         </ul>
@@ -95,7 +96,7 @@
     [Parameter] public required EventCallback<bool> IsDarkModeChanged { get; set; }
 
     private bool _mobileMenuOpen;
-    private bool _dropdownCollapsed;
+    private readonly HashSet<string> _collapsedDropdowns = [];
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
@@ -129,7 +130,7 @@
 
     private void CloseMobileMenu() => _mobileMenuOpen = false;
 
-    private void CollapseDropdown() => _dropdownCollapsed = true;
+    private void CollapseDropdown(string route) => _collapsedDropdowns.Add(route);
 
-    private void ResetDropdown() => _dropdownCollapsed = false;
+    private void ResetDropdown(string route) => _collapsedDropdowns.Remove(route);
 }