Add authentication support with login/logout UI

- Introduced AuthService, IAuthApiClient, and AuthApiClient for managing authentication state and API calls (login, logout, session restore).
- Added Login.razor and LoginLayout.razor for the login page, including styling and logic.
- MainLayout.razor now checks authentication on load, restores sessions from sessionStorage, and redirects to /login if unauthenticated. Displays username and logout button when logged in.
- Implemented JS interop (authStorage) for persisting authentication info in sessionStorage.
- Registered AuthService, CookieContainer, and API clients in Program.cs to share cookies and support authentication.
- Updated AppSettings and appsettings files to support separate ApiBaseUrl and DataApiBaseUrl.
- Minor CSS improvements for username display in the top bar.

DbFirst.BlazorWebApp/AppSettings.cs

@@ -3,4 +3,5 @@
 public class AppSettings
 {
     public string ApiBaseUrl { get; set; } = string.Empty;
+    public string DataApiBaseUrl { get; set; } = string.Empty;
 }