Settings, correção de light/darkmode do dispositivo (e adição da escolha entre modos nas settings) e correção do tipo de letra no textfield do chatbot

lib/main.dart

@@ -4,6 +4,7 @@ import 'package:flutter_localizations/flutter_localizations.dart';
 import 'core/theme/app_theme.dart';
 import 'core/routing/app_router.dart';
 import 'core/services/firebase/firebase_service.dart';
+import 'core/providers/theme_provider.dart';
 import 'l10n/app_localizations.dart';
 
 void main() async {
@@ -15,17 +16,19 @@ void main() async {
   runApp(const ProviderScope(child: MyApp()));
 }
 
-class MyApp extends StatelessWidget {
+class MyApp extends ConsumerWidget {
   const MyApp({super.key});
 
   @override
-  Widget build(BuildContext context) {
+  Widget build(BuildContext context, WidgetRef ref) {
+    final themeMode = ref.watch(themeProvider);
+
     return MaterialApp.router(
       title: 'AI Study Assistant',
       debugShowCheckedModeBanner: false,
       theme: AppTheme.lightTheme,
       darkTheme: AppTheme.darkTheme,
-      themeMode: ThemeMode.system,
+      themeMode: themeMode, // Use theme from provider (currently always light)
       routerConfig: AppRouter.router,
 
       // Internationalization configuration