factory Session.fromJson(Map<String, dynamic> json) {
  // ID: SQLite trả String sometimes
  final rawId = json['empId'] ?? json['id'] ?? 0;
  final id = rawId is int 
    ? rawId 
    : int.tryParse(rawId.toString()) ?? 0;

  // Name: có fallback khi rỗng
  final name = (json['empName'] ?? json['name'] ?? '') as String;

  // Nested employee object
  final emp = json['employee'] as Map<String, dynamic>?;

  return Session(
    id: id,
    name: name.isEmpty ? 'Mới' : name,
    initial: emp?['initial'] as String? ?? json['initial'] as String?,
    colorIdx: emp?['color_idx'] as int? ?? json['color_idx'] as int?,
    role: json['role'] as String? ?? 'employee',
  );
}