feat(acp): add experimental ACP support

Co-authored-by: Jonathan Taylor <visionik@pobox.com>

src/acp/index.ts

@@ -0,0 +1,4 @@
+export { serveAcpGateway } from "./server.js";
+export { createInMemorySessionStore } from "./session.js";
+export type { AcpSessionStore } from "./session.js";
+export type { AcpServerOptions } from "./types.js";