add macOS support for ad loading and improve timestamp handling

lib/main.dart

@@ -1,3 +1,4 @@
+import 'dart:io' show Platform;
 import 'package:flutter/foundation.dart';
 import 'package:go_router/go_router.dart';
 import 'package:quotegen_client/pages/home/page.dart';
@@ -7,8 +8,8 @@ import 'package:google_mobile_ads/google_mobile_ads.dart';
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
 
-  // Initialize mobile ads (AdMob) only on mobile platforms
-  if (!kIsWeb) {
+  // Initialize mobile ads (AdMob) only on mobile platforms (not web or macOS)
+  if (!kIsWeb && !Platform.isMacOS) {
     await MobileAds.instance.initialize();
   }