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/AuthService.cs

@@ -0,0 +1,26 @@
+namespace DbFirst.BlazorWebApp.Services;
+
+public class AuthService
+{
+    public bool IsAuthenticated { get; private set; }
+    public string UserName { get; private set; } = string.Empty;
+    public string? RawCookieHeader { get; private set; }
+
+    public event Action? OnChange;
+
+    public void SetAuthenticated(string userName, string rawCookieHeader)
+    {
+        IsAuthenticated = true;
+        UserName = userName;
+        RawCookieHeader = rawCookieHeader;
+        OnChange?.Invoke();
+    }
+
+    public void SetUnauthenticated()
+    {
+        IsAuthenticated = false;
+        UserName = string.Empty;
+        RawCookieHeader = null;
+        OnChange?.Invoke();
+    }
+}