feat: add server helpers, make connect() to default to parent post transport (#165)

* feat: add server helpers and optional connect() transport

Add `src/server/` with convenience functions for registering MCP App tools
and resources:

- `registerAppTool(server, name, config, handler)`
- `registerAppResource(server, name, uri, config, callback)`

The `transport` parameter in `App.connect()` is now optional, defaulting to
`PostMessageTransport(window.parent)`.

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

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

* Update src/server/index.ts

Co-authored-by: Jonathan Hefner <jonathan@hefner.pro>

* fix: refine server helper types

- Make RESOURCE_URI_META_KEY required in McpUiAppToolConfig (tools need a UI resource)
- Make _meta optional in McpUiAppResourceConfig (not all resources need custom metadata)

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

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

* refactor: simplify RESOURCE_URI_META_KEY re-export

* refactor: consolidate export statements

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jonathan Hefner <jonathan@hefner.pro>

examples/threejs-server/server.ts

@@ -9,7 +9,10 @@ import type { ReadResourceResult } from "@modelcontextprotocol/sdk/types.js";
 import fs from "node:fs/promises";
 import path from "node:path";
 import { z } from "zod";
-import { RESOURCE_MIME_TYPE, RESOURCE_URI_META_KEY } from "../../dist/src/app";
+import {
+  RESOURCE_MIME_TYPE,
+  RESOURCE_URI_META_KEY,
+} from "@modelcontextprotocol/ext-apps/server";
 import { startServer } from "../shared/server-utils.js";
 
 const DIST_DIR = path.join(import.meta.dirname, "dist");
@@ -142,7 +145,8 @@ function createServer(): McpServer {
   });
 
   // Tool 1: show_threejs_scene
-  server.registerTool(
+  registerAppTool(
+    server,
     "show_threejs_scene",
     {
       title: "Show Three.js Scene",
@@ -175,7 +179,8 @@ function createServer(): McpServer {
   );
 
   // Tool 2: learn_threejs
-  server.registerTool(
+  registerAppTool(
+    server,
     "learn_threejs",
     {
       title: "Learn Three.js",
@@ -191,7 +196,8 @@ function createServer(): McpServer {
   );
 
   // Resource registration
-  server.registerResource(
+  registerAppResource(
+    server,
     resourceUri,
     resourceUri,
     { mimeType: RESOURCE_MIME_TYPE, description: "Three.js Widget UI" },