feat: add benefit history feature with lazy loading and pagination

- Implemented `getBenefitsHistory` method in `HomeRepository` to retrieve paginated benefit history.
- Enhanced `BenefitsOverviewCubit` to manage loading and displaying benefit history.
- Created `BenefitHistoryPage` for full-screen display of benefit history with infinite scroll support.
- Added `BenefitHistoryPreview` widget for expandable history preview in benefit cards.
- Introduced `BenefitHistoryRow` to display individual history records.
- Updated `BenefitsOverviewState` to include history management fields.
- Added new entities and use cases for handling benefit history.
- Created design system documentation for UI patterns and known gaps.

apps/mobile/packages/domain/lib/krow_domain.dart

@@ -72,6 +72,7 @@ export 'src/entities/orders/recent_order.dart';
 
 // Financial & Payroll
 export 'src/entities/benefits/benefit.dart';
+export 'src/entities/benefits/benefit_history.dart';
 export 'src/entities/financial/invoice.dart';
 export 'src/entities/financial/billing_account.dart';
 export 'src/entities/financial/current_bill.dart';

apps/mobile/packages/domain/lib/src/entities/benefits/benefit_history.dart

@@ -0,0 +1,100 @@
+import 'package:equatable/equatable.dart';
+
+import 'package:krow_domain/src/entities/enums/benefit_status.dart';
+
+/// A historical record of a staff benefit accrual period.
+///
+/// Returned by `GET /staff/profile/benefits/history`.
+class BenefitHistory extends Equatable {
+  /// Creates a [BenefitHistory] instance.
+  const BenefitHistory({
+    required this.historyId,
+    required this.benefitId,
+    required this.benefitType,
+    required this.title,
+    required this.status,
+    required this.effectiveAt,
+    required this.trackedHours,
+    required this.targetHours,
+    this.endedAt,
+    this.notes,
+  });
+
+  /// Deserialises a [BenefitHistory] from a V2 API JSON map.
+  factory BenefitHistory.fromJson(Map<String, dynamic> json) {
+    return BenefitHistory(
+      historyId: json['historyId'] as String,
+      benefitId: json['benefitId'] as String,
+      benefitType: json['benefitType'] as String,
+      title: json['title'] as String,
+      status: BenefitStatus.fromJson(json['status'] as String?),
+      effectiveAt: DateTime.parse(json['effectiveAt'] as String),
+      endedAt: json['endedAt'] != null
+          ? DateTime.parse(json['endedAt'] as String)
+          : null,
+      trackedHours: (json['trackedHours'] as num).toInt(),
+      targetHours: (json['targetHours'] as num).toInt(),
+      notes: json['notes'] as String?,
+    );
+  }
+
+  /// Unique identifier for this history record.
+  final String historyId;
+
+  /// The benefit this record belongs to.
+  final String benefitId;
+
+  /// Type code (e.g. SICK_LEAVE, VACATION).
+  final String benefitType;
+
+  /// Human-readable title.
+  final String title;
+
+  /// Status of the benefit during this period.
+  final BenefitStatus status;
+
+  /// When this benefit period became effective.
+  final DateTime effectiveAt;
+
+  /// When this benefit period ended, or `null` if still active.
+  final DateTime? endedAt;
+
+  /// Hours tracked during this period.
+  final int trackedHours;
+
+  /// Target hours for this period.
+  final int targetHours;
+
+  /// Optional notes about the accrual.
+  final String? notes;
+
+  /// Serialises this [BenefitHistory] to a JSON map.
+  Map<String, dynamic> toJson() {
+    return <String, dynamic>{
+      'historyId': historyId,
+      'benefitId': benefitId,
+      'benefitType': benefitType,
+      'title': title,
+      'status': status.toJson(),
+      'effectiveAt': effectiveAt.toIso8601String(),
+      'endedAt': endedAt?.toIso8601String(),
+      'trackedHours': trackedHours,
+      'targetHours': targetHours,
+      'notes': notes,
+    };
+  }
+
+  @override
+  List<Object?> get props => <Object?>[
+        historyId,
+        benefitId,
+        benefitType,
+        title,
+        status,
+        effectiveAt,
+        endedAt,
+        trackedHours,
+        targetHours,
+        notes,
+      ];
+}