Center login prompt

lib/widgets/login_prompt.dart

@@ -9,14 +9,17 @@ class LoginPrompt extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Column(
+      mainAxisAlignment: MainAxisAlignment.center,
       children: [
         const Text('Please log in'),
+        const SizedBox(height: 8),
         ElevatedButton(
           onPressed: () {
             Navigator.push(context, MaterialPageRoute(builder: (context) => LoginPage(api: api)));
           },
           child: const Text('Log in'),
         ),
+        const SizedBox(height: 80),
       ],
     );
   }