fix(flutter): 디렉터리 구조를 규칙에 맞추고 깨진 테스트 교체

- 공통 위젯 위치를 lib/widgets/ 에서 규칙상 목표인 lib/shared/widgets/ 로 이동
- 기본 생성된 카운터 위젯 테스트가 실제 앱과 맞지 않아 실패 상태였다 —
  앱 렌더링을 검증하는 테스트로 교체

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

flutter/test/widget_test.dart

@@ -1,30 +1,15 @@
-// This is a basic Flutter widget test.
-//
-// To perform an interaction with a widget in your test, use the WidgetTester
-// utility in the flutter_test package. For example, you can send tap and scroll
-// gestures. You can also use WidgetTester to find child widgets in the widget
-// tree, read text, and verify that the values of widget properties are correct.
-
 import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
-
 import 'package:tma_app/main.dart';
 
 void main() {
-  testWidgets('Counter increments smoke test', (WidgetTester tester) async {
-    // Build our app and trigger a frame.
-    await tester.pumpWidget(const MyApp());
+  testWidgets('앱이 정상적으로 렌더링된다', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const ProviderScope(child: MyApp()),
+    );
 
-    // Verify that our counter starts at 0.
-    expect(find.text('0'), findsOneWidget);
-    expect(find.text('1'), findsNothing);
-
-    // Tap the '+' icon and trigger a frame.
-    await tester.tap(find.byIcon(Icons.add));
-    await tester.pump();
-
-    // Verify that our counter has incremented.
-    expect(find.text('0'), findsNothing);
-    expect(find.text('1'), findsOneWidget);
+    expect(find.byType(MaterialApp), findsOneWidget);
+    expect(find.byType(Scaffold), findsOneWidget);
   });
 }