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/Components/App.razor

@@ -31,6 +31,18 @@
             else
                 document.documentElement.classList.remove('dx-dark');
         };
+
+        window.authStorage = {
+            get: function (key) { return sessionStorage.getItem(key); },
+            set: function (username, cookie) {
+                sessionStorage.setItem('auth_user', username);
+                sessionStorage.setItem('auth_cookie', cookie);
+            },
+            clear: function () {
+                sessionStorage.removeItem('auth_user');
+                sessionStorage.removeItem('auth_cookie');
+            }
+        };
     </script>
     <HeadOutlet />
 </head>