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.Web.Client/Handlers/AuthenticationHeaderHandler.cs

@@ -0,0 +1,27 @@
+using System.Net.Http.Headers;
+using NexusReader.Application.Abstractions.Services;
+
+namespace NexusReader.Web.Client.Handlers;
+
+public class AuthenticationHeaderHandler : DelegatingHandler
+{
+    private readonly INativeStorageService _storageService;
+    private const string TokenKey = "nexus_auth_token";
+
+    public AuthenticationHeaderHandler(INativeStorageService storageService)
+    {
+        _storageService = storageService;
+    }
+
+    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        var tokenResult = await _storageService.GetSecureString(TokenKey);
+        
+        if (tokenResult.IsSuccess && !string.IsNullOrEmpty(tokenResult.Value))
+        {
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", tokenResult.Value);
+        }
+
+        return await base.SendAsync(request, cancellationToken);
+    }
+}