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/threejs-server/test-input.json

@@ -0,0 +1,3 @@
+{
+  "code": "const scene = new THREE.Scene(); const camera = new THREE.PerspectiveCamera(60, width/height, 0.1, 100); camera.position.set(2, 2, 2); camera.lookAt(0, 0.5, 0); const renderer = new THREE.WebGLRenderer({canvas, antialias: true}); renderer.setSize(width, height); renderer.shadowMap.enabled = true; const cube = new THREE.Mesh(new THREE.BoxGeometry(), new THREE.MeshStandardMaterial({color: 0xff4444})); cube.castShadow = true; cube.position.y = 0.5; scene.add(cube); const floor = new THREE.Mesh(new THREE.PlaneGeometry(5,5), new THREE.MeshStandardMaterial({color: 0x222233})); floor.rotation.x = -Math.PI/2; floor.receiveShadow = true; scene.add(floor); const light = new THREE.DirectionalLight(0xffffff, 2); light.position.set(3, 5, 3); light.castShadow = true; scene.add(light); scene.add(new THREE.AmbientLight(0x404040)); function animate() { requestAnimationFrame(animate); cube.rotation.y += 0.01; renderer.render(scene, camera); } animate();"
+}