Refactor code structure for improved readability and maintainability

Co-authored-by: Copilot <copilot@github.com>

flutter/lib/features/profile/domain/user_profile.dart

@@ -0,0 +1,42 @@
+class UserProfile {
+  final int id;
+  final String username;
+  final String email;
+  final String? firstName;
+  final String? lastName;
+  final String role;
+
+  const UserProfile({
+    required this.id,
+    required this.username,
+    required this.email,
+    this.firstName,
+    this.lastName,
+    required this.role,
+  });
+
+  factory UserProfile.fromJson(Map<String, dynamic> json) => UserProfile(
+        id: json['id'] as int,
+        username: json['username'] as String,
+        email: json['email'] as String? ?? '',
+        firstName: json['firstName'] as String?,
+        lastName: json['lastName'] as String?,
+        role: json['role'] as String? ?? 'user',
+      );
+
+  bool get isAdmin => role == 'admin';
+
+  UserProfile copyWith({
+    String? email,
+    String? firstName,
+    String? lastName,
+  }) =>
+      UserProfile(
+        id: id,
+        username: username,
+        email: email ?? this.email,
+        firstName: firstName ?? this.firstName,
+        lastName: lastName ?? this.lastName,
+        role: role,
+      );
+}