feat: implement asynchronous text selection summarization with real-time UI updates and skeleton loading states

src/NexusReader.UI.Shared/Services/KnowledgeCoordinator.cs

@@ -22,12 +22,21 @@ public sealed partial class KnowledgeCoordinator : IDisposable, IAsyncDisposable
     
     public string CurrentFullPageContent { get; private set; } = string.Empty;
     
+    public bool IsLoadingSelectionSummary { get; private set; }
+    public string? SelectionSummary { get; private set; }
+    public string? SelectedTextContext { get; private set; }
+    
     /// <summary>
     /// Raised when the knowledge graph has been updated with new data.
     /// Subscribers must return a Task to enable proper async handling.
     /// </summary>
     public event Func<GraphDataDto, Task>? OnGraphUpdated;
 
+    /// <summary>
+    /// Raised when the selection summary state has changed (loading started, finished, or cleared).
+    /// </summary>
+    public event Func<Task>? OnSelectionSummaryStateChanged;
+
     public KnowledgeCoordinator(
         IKnowledgeService knowledgeService,
         IKnowledgeGraphService graphService,
@@ -205,6 +214,47 @@ public sealed partial class KnowledgeCoordinator : IDisposable, IAsyncDisposable
         }
     }
 
+    public async Task StartSelectionSummaryAsync(string text, string tenantId = "global")
+    {
+        if (string.IsNullOrWhiteSpace(text)) return;
+        
+        IsLoadingSelectionSummary = true;
+        SelectionSummary = null;
+        SelectedTextContext = text;
+        if (OnSelectionSummaryStateChanged != null)
+        {
+            await OnSelectionSummaryStateChanged.Invoke();
+        }
+
+        try
+        {
+            var result = await RequestSummaryAndQuizAsync(text, tenantId);
+            if (result.IsSuccess)
+            {
+                SelectionSummary = result.Value.Summary;
+            }
+        }
+        finally
+        {
+            IsLoadingSelectionSummary = false;
+            if (OnSelectionSummaryStateChanged != null)
+            {
+                await OnSelectionSummaryStateChanged.Invoke();
+            }
+        }
+    }
+
+    public async Task ClearSelectionSummaryAsync()
+    {
+        SelectionSummary = null;
+        SelectedTextContext = null;
+        IsLoadingSelectionSummary = false;
+        if (OnSelectionSummaryStateChanged != null)
+        {
+            await OnSelectionSummaryStateChanged.Invoke();
+        }
+    }
+
     public async Task ClearAsync()
     {
         CancelAndDisposeCts(ref _graphCts);
@@ -213,6 +263,7 @@ public sealed partial class KnowledgeCoordinator : IDisposable, IAsyncDisposable
         CurrentFullPageContent = string.Empty;
         await _graphService.Clear();
         await _quizService.SetQuiz(null, null);
+        await ClearSelectionSummaryAsync();
     }
 
     public void Dispose()