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/src/global.css

@@ -0,0 +1,43 @@
+* {
+  box-sizing: border-box;
+}
+
+html, body {
+  font-family: system-ui, -apple-system, sans-serif;
+  font-size: 1rem;
+  margin: 0;
+  padding: 0;
+  background: #1a1a2e;
+}
+
+.loading {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  height: 400px;
+  color: #888;
+  font-size: 14px;
+}
+
+.error {
+  padding: 20px;
+  color: #ff6b6b;
+}
+
+.threejs-container {
+  width: 100%;
+  position: relative;
+}
+
+.error-overlay {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  color: #ff6b6b;
+  background: rgba(26, 26, 46, 0.9);
+  border-radius: 8px;
+  font-family: system-ui;
+  padding: 20px;
+}