release: align the repo version with the shipped 0.2.1 and guard future tags (#219)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/core/src/index.ts

@@ -59,7 +59,7 @@ export { Agent, createAgent } from "./agent.js";
 export type { CreateAgentOptions, CreateSessionOptions, ResumeSessionOptions } from "./agent.js";
 
 /** SDK version number. */
-export const VERSION = "0.2.0";
+export const VERSION = "0.2.1";
 /** Release build date (UTC yyyy-mm-dd), stamped by the release workflow next to VERSION; null in a dev/source build. */
 export const BUILD_DATE: string | null = null;
 // Version-string helpers (shared by the CLI's `penguin update` and the server's update check).