Create placeholder SkillTreeView

frontend/lib/views/skill_tree/skill_tree_view.dart

@@ -0,0 +1,21 @@
+import 'package:flutter/material.dart';
+
+class SkillTreeView extends StatelessWidget {
+  const SkillTreeView({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      color: Colors.blue[100], // Background color
+      child: const Center(
+        child: Text(
+          'SkillTreeView',
+          style: TextStyle(
+            fontSize: 24,
+            fontWeight: FontWeight.bold,
+          ),
+        ),
+      ),
+    );
+  }
+}