Add Three.js marketing example server

New example demonstrating interactive 3D scene rendering with:
- show_threejs_scene tool with streaming code preview
- learn_threejs documentation tool
- Full WidgetProps interface for MCP App integration
- Reusable mcp-app-wrapper.tsx pattern

Also adds bun.lockb to .gitignore.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/basic-host/src/index.tsx

@@ -13,6 +13,7 @@ const SERVERS = [
   { name: "Customer Segmentation", port: 3105 },
   { name: "Scenario Modeler", port: 3106 },
   { name: "System Monitor", port: 3107 },
+  { name: "Three.js", port: 3109 },
 ] as const;
 
 function serverUrl(port: number): string {