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>

src/app.ts

@@ -16,6 +16,7 @@ import {
   PingRequestSchema,
 } from "@modelcontextprotocol/sdk/types.js";
 import { AppNotification, AppRequest, AppResult } from "./types";
+import { PostMessageTransport } from "./message-transport";
 import {
   LATEST_PROTOCOL_VERSION,
   McpUiAppCapabilities,
@@ -1025,7 +1026,7 @@ export class App extends Protocol<AppRequest, AppNotification, AppResult> {
    * @see {@link PostMessageTransport} for the typical transport implementation
    */
   override async connect(
-    transport: Transport,
+    transport: Transport = new PostMessageTransport(window.parent),
     options?: RequestOptions,
   ): Promise<void> {
     await super.connect(transport);