Refactor Intelligence Toolbar (#14) and fix auth regression (#24)

This PR resolves the authentication regression issue where users encountered "Unauthorized" errors after logging out and back in. This regression was identified during the refactoring of the Intelligence Toolbar.

Fixes #14

### Changes:
- **WASM Client**: Added `AuthenticationHeaderHandler` to automatically attach Bearer tokens to `HttpClient` requests.
- **Server**: Configured Cookie authentication to return `401 Unauthorized` for `/api` requests instead of redirecting to the login page.
- **Project Configuration**: Added `Microsoft.Extensions.Http` to the WASM client project to support `IHttpClientFactory` and message handlers.

Verified with local build.

Reviewed-on: #24
Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-committed-by: Marek Jasiński <jasins.marek@gmail.com>

src/NexusReader.UI.Shared/Components/Molecules/IntelligenceToolbar.razor

@@ -2,6 +2,8 @@
 @using NexusReader.Application.Abstractions.Services
 @inject IFocusModeService FocusMode
 @inject IKnowledgeService KnowledgeService
+@inject IIdentityService IdentityService
+@inject NavigationManager NavigationManager
 
 <aside class="intelligence-toolbar">
     <div class="toolbar-top">
@@ -36,6 +38,9 @@
         <button class="toolbar-item" title="Global Settings">
             <NexusIcon Name="settings" Size="20" />
         </button>
+        <button class="toolbar-item logout-item" @onclick="HandleLogout" title="Logout">
+            <NexusIcon Name="log-out" Size="20" />
+        </button>
     </div>
 </aside>
 
@@ -56,6 +61,12 @@
         }
     }
 
+    private async Task HandleLogout()
+    {
+        await IdentityService.LogoutAsync();
+        NavigationManager.NavigateTo("/", true);
+    }
+
     private Task HandleUpdate() => InvokeAsync(StateHasChanged);
 
     public void Dispose()