fix: address PR review — await store.cas.put + bun shebang → node

- Add missing await on store.cas.put() in run.ts:192
- Replace #!/usr/bin/env bun → #!/usr/bin/env node in all CLI bins
- Update issue-551 test to assert node shebang

packages/agent-builtin/src/cli.ts

@@ -1,4 +1,4 @@
-#!/usr/bin/env bun
+#!/usr/bin/env node
 
 import { createBuiltinAgent } from "./agent.js";