Simplify theme management, integrate ToggleButtons for theme selection, and enhance settings view structure.

finlog_app/app/lib/main.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:fluttery/fluttery.dart';
 import 'package:fluttery/logger.dart';
 import 'package:go_router/go_router.dart';
+import 'package:provider/provider.dart';
 
 Future<void> main() async {
   // Ensures that the Flutter engine and widget binding
@@ -25,9 +26,12 @@ Future<void> main() async {
   await themeController.init();
 
   runApp(
-    FinlogApp(
-      router: buildAppRouter(startRoute),
-      themeController: themeController,
+    MultiProvider(
+      providers: [ChangeNotifierProvider(create: (context) => themeController)],
+      child: FinlogApp(
+        router: buildAppRouter(startRoute),
+        themeController: themeController,
+      ),
     ),
   );
 }