feat(approvals): Approval Flow v2 프런트엔드 전면 개편

- 환경/라우터 모듈에 approval_flow_v2 토글을 추가하고 FeatureFlags 초기화를 연결 (.env*, lib/core/**)
- ApiClient 빌더·ApiRoutes 확장과 ApprovalRepositoryRemote 리팩터링으로 include·액션 시그니처를 정합화
- ApprovalFlow·ApprovalDraft 엔티티/레포/유즈케이스를 도입해 서버 초안과 단계 액션(승인·회수·재상신)을 지원
- Approval 컨트롤러·히스토리·템플릿 페이지와 공유 위젯을 재작성해 감사 로그·회수 UX·템플릿 CRUD를 반영
- Inbound/Outbound/Rental 컨트롤러·페이지에 결재 섹션을 삽입하고 대시보드 pending 카드 요약을 갱신
- SuperportDialog·FormField 등 공통 위젯을 보강하고 승인 위젯 가이드를 추가해 UI 가이드를 정리
- 결재/재고 테스트 픽스처와 단위·위젯·통합 테스트를 확장하고 flutter_test_config로 스테이징 호스트를 허용
- Approval Flow 레포트/플랜 문서를 업데이트하고 ApprovalFlow_System_Integration_and_ChangePlan.md를 추가
- 실행: flutter analyze, flutter test

lib/features/inventory/rental/presentation/pages/rental_page.dart

@@ -17,6 +17,13 @@ import 'package:superport_v2/features/inventory/shared/widgets/product_autocompl
 import 'package:superport_v2/features/inventory/shared/widgets/employee_autocomplete_field.dart';
 import 'package:superport_v2/features/inventory/shared/widgets/customer_multi_select_field.dart';
 import 'package:superport_v2/features/inventory/shared/widgets/warehouse_select_field.dart';
+import 'package:superport_v2/features/approvals/request/presentation/controllers/approval_request_controller.dart';
+import 'package:superport_v2/features/approvals/request/presentation/utils/approval_form_initializer.dart';
+import 'package:superport_v2/features/approvals/request/presentation/widgets/approval_step_configurator.dart';
+import 'package:superport_v2/features/approvals/request/presentation/widgets/approval_template_picker.dart';
+import 'package:superport_v2/features/approvals/domain/usecases/get_approval_draft_use_case.dart';
+import 'package:superport_v2/features/approvals/domain/usecases/list_approval_drafts_use_case.dart';
+import 'package:superport_v2/features/approvals/domain/usecases/save_approval_draft_use_case.dart';
 import 'package:superport_v2/core/config/environment.dart';
 import 'package:superport_v2/core/network/failure.dart';
 import 'package:superport_v2/core/permissions/permission_manager.dart';
@@ -29,6 +36,7 @@ import 'package:superport_v2/features/inventory/transactions/domain/entities/sto
 import 'package:superport_v2/features/inventory/transactions/domain/repositories/stock_transaction_repository.dart';
 import 'package:superport_v2/features/inventory/transactions/presentation/services/transaction_detail_sync_service.dart';
 import 'package:superport_v2/features/inventory/transactions/presentation/widgets/transaction_detail_dialog.dart';
+import 'package:superport_v2/features/auth/application/auth_service.dart';
 import '../../../lookups/domain/entities/lookup_item.dart';
 import '../../../lookups/domain/repositories/inventory_lookup_repository.dart';
 import '../widgets/rental_detail_view.dart';
@@ -130,6 +138,15 @@ class _RentalPageState extends State<RentalPage> {
       fallbackStatusOptions: RentalTableSpec.fallbackStatusOptions,
       rentTransactionKeywords: RentalTableSpec.rentTransactionKeywords,
       returnTransactionKeywords: RentalTableSpec.returnTransactionKeywords,
+      saveDraftUseCase: getIt.isRegistered<SaveApprovalDraftUseCase>()
+          ? getIt<SaveApprovalDraftUseCase>()
+          : null,
+      getDraftUseCase: getIt.isRegistered<GetApprovalDraftUseCase>()
+          ? getIt<GetApprovalDraftUseCase>()
+          : null,
+      listDraftsUseCase: getIt.isRegistered<ListApprovalDraftsUseCase>()
+          ? getIt<ListApprovalDraftsUseCase>()
+          : null,
     );
   }
 
@@ -140,6 +157,10 @@ class _RentalPageState extends State<RentalPage> {
     }
     Future.microtask(() async {
       await controller.loadStatusOptions();
+      final requester = _resolveCurrentWriter();
+      if (requester != null) {
+        await controller.loadApprovalDraftFromServer(requesterId: requester.id);
+      }
       final hasTypes = await controller.resolveTransactionTypes();
       if (!mounted) {
         return;
@@ -219,6 +240,26 @@ class _RentalPageState extends State<RentalPage> {
     }
   }
 
+  InventoryEmployeeSuggestion? _resolveCurrentWriter() {
+    final getIt = GetIt.I;
+    if (!getIt.isRegistered<AuthService>()) {
+      return null;
+    }
+    final session = getIt<AuthService>().session;
+    final user = session?.user;
+    if (user == null) {
+      return null;
+    }
+    final employeeNo = (user.employeeNo ?? '').trim().isEmpty
+        ? user.id.toString()
+        : user.employeeNo!.trim();
+    return InventoryEmployeeSuggestion(
+      id: user.id,
+      employeeNo: employeeNo,
+      name: user.name,
+    );
+  }
+
   @override
   void didUpdateWidget(covariant RentalPage oldWidget) {
     super.didUpdateWidget(oldWidget);
@@ -1538,6 +1579,25 @@ class _RentalPageState extends State<RentalPage> {
       return '${suggestion.name} (${suggestion.employeeNo})';
     }
 
+    final approvalController = ApprovalRequestController();
+    final defaultRequester = () {
+      final writer = writerSelection;
+      if (writer == null) {
+        return null;
+      }
+      return ApprovalRequestParticipant(
+        id: writer.id,
+        name: writer.name,
+        employeeNo: writer.employeeNo,
+      );
+    }();
+    ApprovalFormInitializer.populate(
+      controller: approvalController,
+      existingApproval: initial?.raw?.approval,
+      draft: _controller?.approvalDraft,
+      defaultRequester: defaultRequester,
+    );
+
     final writerController = TextEditingController(
       text: writerLabel(writerSelection),
     );
@@ -1792,6 +1852,23 @@ class _RentalPageState extends State<RentalPage> {
             )
             .toList(growable: false);
 
+        StockTransactionApprovalInput approvalInput;
+        try {
+          approvalInput = approvalController.buildTransactionApprovalInput(
+            approvalStatusId: null,
+            note: approvalNoteValue.isEmpty ? null : approvalNoteValue,
+          );
+        } on StateError catch (error) {
+          updateSaving(false);
+          SuperportToast.error(context, error.message);
+          return;
+        } catch (_) {
+          updateSaving(false);
+          SuperportToast.error(context, '결재 구성을 확인하고 다시 시도하세요.');
+          return;
+        }
+        controller.updateApprovalDraft(approvalInput);
+
         final transactionTypeId = selectedLookup.id;
         final created = await controller.createTransaction(
           StockTransactionCreateInput(
@@ -1804,10 +1881,7 @@ class _RentalPageState extends State<RentalPage> {
             expectedReturnDate: returnDue.value,
             lines: createLines,
             customers: createCustomers,
-            approval: StockTransactionApprovalInput(
-              requestedById: createdById,
-              note: approvalNoteValue.isEmpty ? null : approvalNoteValue,
-            ),
+            approval: approvalInput,
           ),
         );
         result = created;
@@ -2093,6 +2167,15 @@ class _RentalPageState extends State<RentalPage> {
                               enabled: initial == null,
                               onSuggestionSelected: (suggestion) {
                                 writerSelection = suggestion;
+                                approvalController.setRequester(
+                                  suggestion == null
+                                      ? null
+                                      : ApprovalRequestParticipant(
+                                          id: suggestion.id,
+                                          name: suggestion.name,
+                                          employeeNo: suggestion.employeeNo,
+                                        ),
+                                );
                                 if (writerError != null) {
                                   setState(() {
                                     writerError = null;
@@ -2109,6 +2192,7 @@ class _RentalPageState extends State<RentalPage> {
                                   if (currentText.isEmpty ||
                                       currentText != selectedLabel) {
                                     writerSelection = null;
+                                    approvalController.setRequester(null);
                                   }
                                   if (writerError != null) {
                                     setState(() {
@@ -2154,6 +2238,15 @@ class _RentalPageState extends State<RentalPage> {
                     ),
                   ],
                 ),
+                const SizedBox(height: 16),
+                if (initial == null) ...[
+                  ApprovalTemplatePicker(controller: approvalController),
+                  const SizedBox(height: 16),
+                ],
+                ApprovalStepConfigurator(
+                  controller: approvalController,
+                  readOnly: initial != null,
+                ),
                 const SizedBox(height: 24),
                 Wrap(
                   spacing: 12,
@@ -2274,6 +2367,7 @@ class _RentalPageState extends State<RentalPage> {
     approvalNoteController.dispose();
     processedAt.dispose();
     returnDue.dispose();
+    approvalController.dispose();
 
     return result;
   }