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/features/approvals/domain/entities/approval_template.dart

@@ -0,0 +1,64 @@
+/// 결재 템플릿 엔티티
+///
+/// - 반복되는 결재 단계를 사전에 정의해두고 요청 시 불러온다.
+class ApprovalTemplate {
+  ApprovalTemplate({
+    required this.id,
+    required this.code,
+    required this.name,
+    this.description,
+    required this.isActive,
+    this.createdBy,
+    this.createdAt,
+    this.updatedAt,
+    this.steps = const [],
+  });
+
+  final int id;
+  final String code;
+  final String name;
+  final String? description;
+  final bool isActive;
+  final ApprovalTemplateAuthor? createdBy;
+  final DateTime? createdAt;
+  final DateTime? updatedAt;
+  final List<ApprovalTemplateStep> steps;
+}
+
+class ApprovalTemplateAuthor {
+  ApprovalTemplateAuthor({
+    required this.id,
+    required this.employeeNo,
+    required this.name,
+  });
+
+  final int id;
+  final String employeeNo;
+  final String name;
+}
+
+class ApprovalTemplateStep {
+  ApprovalTemplateStep({
+    this.id,
+    required this.stepOrder,
+    required this.approver,
+    this.note,
+  });
+
+  final int? id;
+  final int stepOrder;
+  final ApprovalTemplateApprover approver;
+  final String? note;
+}
+
+class ApprovalTemplateApprover {
+  ApprovalTemplateApprover({
+    required this.id,
+    required this.employeeNo,
+    required this.name,
+  });
+
+  final int id;
+  final String employeeNo;
+  final String name;
+}