Add cookie/JWT-based authentication and user context headers

Introduce a new authentication mechanism using JWT tokens stored in cookies, with a custom CookieAuthHandler for API request authentication. Add AuthServiceSettings for configuration and UserHeaderHandler to propagate user context in outgoing HTTP requests. Update service registrations and configuration files to support the new authentication flow. Refactor CurrentUserService for simplicity. This enables stateless, cookie-based authentication and consistent user context across API calls.

DbFirst.BlazorWebApp/Services/UserHeaderHandler.cs

@@ -0,0 +1,17 @@
+namespace DbFirst.BlazorWebApp.Services;
+
+public class UserHeaderHandler(AuthService authService) : DelegatingHandler
+{
+    protected override Task<HttpResponseMessage> SendAsync(
+        HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        if (authService.IsAuthenticated)
+        {
+            request.Headers.TryAddWithoutValidation("X-Authenticated-User", authService.UserName);
+            if (!string.IsNullOrEmpty(authService.RawCookieHeader))
+                request.Headers.TryAddWithoutValidation("Cookie", authService.RawCookieHeader);
+        }
+
+        return base.SendAsync(request, cancellationToken);
+    }
+}