feat: 회사 관리 API 연동 구현

- CompanyService 및 RemoteDataSource 구현
- Company, Branch DTO 모델 생성 (Freezed)
- 의존성 주입 컨테이너 업데이트
- 회사 등록/수정 폼에 API 연동 로직 적용
- API 통합 계획 문서 업데이트

lib/data/models/company/branch_dto.dart

@@ -0,0 +1,69 @@
+import 'package:freezed_annotation/freezed_annotation.dart';
+
+part 'branch_dto.freezed.dart';
+part 'branch_dto.g.dart';
+
+@freezed
+class CreateBranchRequest with _$CreateBranchRequest {
+  const factory CreateBranchRequest({
+    @JsonKey(name: 'branch_name') required String branchName,
+    required String address,
+    required String phone,
+    @JsonKey(name: 'manager_name') String? managerName,
+    @JsonKey(name: 'manager_phone') String? managerPhone,
+    String? remark,
+  }) = _CreateBranchRequest;
+
+  factory CreateBranchRequest.fromJson(Map<String, dynamic> json) =>
+      _$CreateBranchRequestFromJson(json);
+}
+
+@freezed
+class UpdateBranchRequest with _$UpdateBranchRequest {
+  const factory UpdateBranchRequest({
+    @JsonKey(name: 'branch_name') String? branchName,
+    String? address,
+    String? phone,
+    @JsonKey(name: 'manager_name') String? managerName,
+    @JsonKey(name: 'manager_phone') String? managerPhone,
+    String? remark,
+  }) = _UpdateBranchRequest;
+
+  factory UpdateBranchRequest.fromJson(Map<String, dynamic> json) =>
+      _$UpdateBranchRequestFromJson(json);
+}
+
+@freezed
+class BranchResponse with _$BranchResponse {
+  const factory BranchResponse({
+    required int id,
+    @JsonKey(name: 'company_id') required int companyId,
+    @JsonKey(name: 'branch_name') required String branchName,
+    required String address,
+    required String phone,
+    @JsonKey(name: 'manager_name') String? managerName,
+    @JsonKey(name: 'manager_phone') String? managerPhone,
+    String? remark,
+    @JsonKey(name: 'created_at') required DateTime createdAt,
+    @JsonKey(name: 'updated_at') required DateTime updatedAt,
+    @JsonKey(name: 'address_id') int? addressId,
+  }) = _BranchResponse;
+
+  factory BranchResponse.fromJson(Map<String, dynamic> json) =>
+      _$BranchResponseFromJson(json);
+}
+
+@freezed
+class BranchListDto with _$BranchListDto {
+  const factory BranchListDto({
+    required int id,
+    @JsonKey(name: 'company_id') required int companyId,
+    @JsonKey(name: 'branch_name') required String branchName,
+    required String address,
+    required String phone,
+    @JsonKey(name: 'manager_name') String? managerName,
+  }) = _BranchListDto;
+
+  factory BranchListDto.fromJson(Map<String, dynamic> json) =>
+      _$BranchListDtoFromJson(json);
+}