feat(ui): add sessionStorage persistence for TreeView expansion state (R11)

src/ScadaLink.CentralUI/Components/Shared/TreeView.razor

@@ -1,5 +1,6 @@
 @* Reusable hierarchical tree view with expand/collapse, ARIA roles, and guide lines *@
 @typeparam TItem
+@inject IJSRuntime JSRuntime
 
 @if (_items is null || _items.Count == 0)
 {
@@ -58,6 +59,7 @@ else
     private IReadOnlyList<TItem>? _items;
     private HashSet<object> _expandedKeys = new();
     private bool _initialExpansionApplied;
+    private bool _storageLoaded;
 
     [Parameter, EditorRequired] public IReadOnlyList<TItem> Items { get; set; } = [];
     [Parameter, EditorRequired] public Func<TItem, IReadOnlyList<TItem>> ChildrenSelector { get; set; } = default!;
@@ -72,6 +74,7 @@ else
     [Parameter] public object? SelectedKey { get; set; }
     [Parameter] public EventCallback<object?> SelectedKeyChanged { get; set; }
     [Parameter] public string SelectedCssClass { get; set; } = "bg-primary bg-opacity-10";
+    [Parameter] public string? StorageKey { get; set; }
 
     protected override void OnParametersSet()
     {
@@ -79,8 +82,40 @@ else
 
         if (!_initialExpansionApplied && InitiallyExpanded != null && _items is { Count: > 0 })
         {
-            _initialExpansionApplied = true;
-            ApplyInitialExpansion(_items);
+            // Only apply InitiallyExpanded when there is no StorageKey, or storage
+            // has already been checked and returned nothing (no prior state).
+            if (StorageKey == null || (_storageLoaded && _expandedKeys.Count == 0))
+            {
+                _initialExpansionApplied = true;
+                ApplyInitialExpansion(_items);
+            }
+        }
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender && StorageKey != null)
+        {
+            var json = await JSRuntime.InvokeAsync<string?>("treeviewStorage.load", StorageKey);
+            _storageLoaded = true;
+
+            if (json != null)
+            {
+                var keys = System.Text.Json.JsonSerializer.Deserialize<List<string>>(json);
+                if (keys != null)
+                {
+                    _expandedKeys = new HashSet<object>(keys);
+                    _initialExpansionApplied = true;
+                }
+            }
+            else if (InitiallyExpanded != null && _items is { Count: > 0 } && !_initialExpansionApplied)
+            {
+                // Storage returned null (no prior state) — fall back to InitiallyExpanded
+                _initialExpansionApplied = true;
+                ApplyInitialExpansion(_items);
+            }
+
+            StateHasChanged();
         }
     }
 
@@ -107,6 +142,18 @@ else
         {
             _expandedKeys.Add(key);
         }
+
+        PersistExpandedState();
+    }
+
+    private void PersistExpandedState()
+    {
+        if (StorageKey != null)
+        {
+            var keys = _expandedKeys.Select(k => k.ToString()!).ToList();
+            var json = System.Text.Json.JsonSerializer.Serialize(keys);
+            _ = JSRuntime.InvokeVoidAsync("treeviewStorage.save", StorageKey, json);
+        }
     }
 
     private async Task OnContentClick(object key)