Update SkillTreeNode data model for skill tree

The SkillTreeNode model represents a single node in the skill tree.
It includes:
- Node ID
- Node color

frontend/lib/models/skill_tree/skill_tree_node.dart

@@ -0,0 +1,18 @@
+import 'package:auto_gpt_flutter_client/models/skill_tree/skill_node_data.dart';
+
+// TODO: Update this with actual data
+class SkillTreeNode {
+  final String color;
+  final int id;
+
+  // final SkillNodeData data;
+
+  SkillTreeNode({required this.color, required this.id});
+
+  factory SkillTreeNode.fromJson(Map<String, dynamic> json) {
+    return SkillTreeNode(
+      color: json['color'],
+      id: json['id'],
+    );
+  }
+}