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/Layout/MainLayout.razor

@@ -35,10 +35,7 @@
                             <span>Asystent AI</span>
                         </div>
 
-                        <div class="user-profile">
-                            <span class="user-email">@context.User.Identity?.Name</span>
-                            <button class="logout-btn" @onclick="HandleLogout">Logout</button>
-                        </div>
+
 
                         <button class="close-btn">×</button>
                     </div>
@@ -93,11 +90,7 @@
         }
     }
 
-    private async Task HandleLogout()
-    {
-        await IdentityService.LogoutAsync();
-        NavigationManager.NavigateTo("/", true);
-    }
+
 
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {