결재 템플릿 단계 적용 구현

- ApprovalTemplate 엔티티·DTO·원격 리포지토리 추가
- ApprovalController에 템플릿 로딩/적용 상태와 assignSteps 호출 연동
- ApprovalPage 단계 탭에 템플릿 선택 UI 및 적용 확인 다이얼로그 구현
- 템플릿 적용 단위 테스트와 IMPLEMENTATION_TASKS 현황 갱신

lib/widgets/components/coming_soon_card.dart

@@ -0,0 +1,49 @@
+import 'package:flutter/widgets.dart';
+import 'package:shadcn_ui/shadcn_ui.dart';
+
+/// 구축 예정인 화면에 안내 메시지를 제공하는 카드 위젯.
+class ComingSoonCard extends StatelessWidget {
+  const ComingSoonCard({
+    super.key,
+    required this.title,
+    required this.description,
+    this.items = const <String>[],
+  });
+
+  final String title;
+  final String description;
+  final List<String> items;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = ShadTheme.of(context);
+
+    return ShadCard(
+      child: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Text(title, style: theme.textTheme.h3),
+            const SizedBox(height: 12),
+            Text(description, style: theme.textTheme.p),
+            if (items.isNotEmpty) ...[
+              const SizedBox(height: 16),
+              for (final item in items)
+                Padding(
+                  padding: const EdgeInsets.only(top: 8),
+                  child: Row(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: [
+                      const Text('• '),
+                      Expanded(child: Text(item, style: theme.textTheme.p)),
+                    ],
+                  ),
+                ),
+            ],
+          ],
+        ),
+      ),
+    );
+  }
+}