Added core data models, repositories, and utilities

lifetimer/lib/data/models/goal_step_model.dart

@@ -0,0 +1,62 @@
+import 'package:equatable/equatable.dart';
+
+class GoalStep extends Equatable {
+  final String id;
+  final String goalId;
+  final String title;
+  final bool isDone;
+  final int orderIndex;
+  final DateTime createdAt;
+
+  const GoalStep({
+    required this.id,
+    required this.goalId,
+    required this.title,
+    required this.isDone,
+    required this.orderIndex,
+    required this.createdAt,
+  });
+
+  GoalStep copyWith({
+    String? id,
+    String? goalId,
+    String? title,
+    bool? isDone,
+    int? orderIndex,
+    DateTime? createdAt,
+  }) {
+    return GoalStep(
+      id: id ?? this.id,
+      goalId: goalId ?? this.goalId,
+      title: title ?? this.title,
+      isDone: isDone ?? this.isDone,
+      orderIndex: orderIndex ?? this.orderIndex,
+      createdAt: createdAt ?? this.createdAt,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'goal_id': goalId,
+      'title': title,
+      'is_done': isDone,
+      'order_index': orderIndex,
+      'created_at': createdAt.toIso8601String(),
+    };
+  }
+
+  factory GoalStep.fromJson(Map<String, dynamic> json) {
+    return GoalStep(
+      id: json['id'] as String,
+      goalId: json['goal_id'] as String,
+      title: json['title'] as String,
+      isDone: json['is_done'] as bool? ?? false,
+      orderIndex: json['order_index'] as int? ?? 0,
+      createdAt: DateTime.parse(json['created_at'] as String),
+    );
+  }
+
+  @override
+  List<Object?> get props => [id, goalId, title, isDone, orderIndex, createdAt];
+}