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/Services/IAuthApiClient.cs

@@ -0,0 +1,8 @@
+namespace DbFirst.BlazorWebApp.Services;
+
+public interface IAuthApiClient
+{
+    Task<bool> LoginAsync(string username, string password, CancellationToken ct = default);
+    Task LogoutAsync(CancellationToken ct = default);
+    Task<bool> RestoreAsync(string username, string rawCookieHeader, CancellationToken ct = default);
+}