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/mcp-app-wrapper.tsx

@@ -0,0 +1,119 @@
+/**
+ * Three.js Widget - MCP App Wrapper
+ *
+ * Generic wrapper that handles MCP App connection and passes all relevant
+ * props to the actual widget component.
+ */
+import type { App, McpUiHostContext } from "@modelcontextprotocol/ext-apps";
+import { useApp } from "@modelcontextprotocol/ext-apps/react";
+import type { CallToolResult } from "@modelcontextprotocol/sdk/types.js";
+import { StrictMode, useState, useCallback } from "react";
+import { createRoot } from "react-dom/client";
+import ThreeJSApp from "./threejs-app.tsx";
+import "./global.css";
+
+const APP_INFO = { name: "Three.js Widget", version: "1.0.0" };
+
+/**
+ * Props passed to the widget component.
+ * This interface can be reused for other widgets.
+ */
+export interface WidgetProps<TToolInput = Record<string, unknown>> {
+  /** Complete tool input (after streaming finishes) */
+  toolInputs: TToolInput | null;
+  /** Partial tool input (during streaming) */
+  toolInputsPartial: TToolInput | null;
+  /** Tool execution result from the server */
+  toolResult: CallToolResult | null;
+  /** Host context (theme, viewport, locale, etc.) */
+  hostContext: McpUiHostContext | null;
+  /** Call a tool on the MCP server */
+  callServerTool: App["callServerTool"];
+  /** Send a message to the host's chat */
+  sendMessage: App["sendMessage"];
+  /** Request the host to open a URL */
+  sendOpenLink: App["sendOpenLink"];
+  /** Send log messages to the host */
+  sendLog: App["sendLog"];
+}
+
+function McpAppWrapper() {
+  const [toolInputs, setToolInputs] = useState<Record<string, unknown> | null>(
+    null,
+  );
+  const [toolInputsPartial, setToolInputsPartial] = useState<Record<
+    string,
+    unknown
+  > | null>(null);
+  const [toolResult, setToolResult] = useState<CallToolResult | null>(null);
+  const [hostContext, setHostContext] = useState<McpUiHostContext | null>(null);
+
+  const { app, error } = useApp({
+    appInfo: APP_INFO,
+    capabilities: {},
+    onAppCreated: (app) => {
+      // Complete tool input (streaming finished)
+      app.ontoolinput = (params) => {
+        setToolInputs(params.arguments as Record<string, unknown>);
+        setToolInputsPartial(null);
+      };
+      // Partial tool input (streaming in progress)
+      app.ontoolinputpartial = (params) => {
+        setToolInputsPartial(params.arguments as Record<string, unknown>);
+      };
+      // Tool execution result
+      app.ontoolresult = (params) => {
+        setToolResult(params as CallToolResult);
+      };
+      // Host context changes (theme, viewport, etc.)
+      app.onhostcontextchanged = (params) => {
+        setHostContext(params);
+      };
+    },
+  });
+
+  // Memoized callbacks that forward to app methods
+  const callServerTool = useCallback<App["callServerTool"]>(
+    (params, options) => app!.callServerTool(params, options),
+    [app],
+  );
+  const sendMessage = useCallback<App["sendMessage"]>(
+    (params, options) => app!.sendMessage(params, options),
+    [app],
+  );
+  const sendOpenLink = useCallback<App["sendOpenLink"]>(
+    (params, options) => app!.sendOpenLink(params, options),
+    [app],
+  );
+  const sendLog = useCallback<App["sendLog"]>(
+    (params) => app!.sendLog(params),
+    [app],
+  );
+
+  if (error) {
+    return <div className="error">Error: {error.message}</div>;
+  }
+
+  if (!app) {
+    return <div className="loading">Connecting...</div>;
+  }
+
+  return (
+    <ThreeJSApp
+      toolInputs={toolInputs}
+      toolInputsPartial={toolInputsPartial}
+      toolResult={toolResult}
+      hostContext={hostContext}
+      callServerTool={callServerTool}
+      sendMessage={sendMessage}
+      sendOpenLink={sendOpenLink}
+      sendLog={sendLog}
+    />
+  );
+}
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <McpAppWrapper />
+  </StrictMode>,
+);