docs: clarify event-driven action examples

[aose-yuu]

Purpose

Clarify the controlled molecule examples so child molecules expose user intent actions instead of owner-style setters.

Summary

• Uses open, close, and toggle as the public dialog actions.
• Keeps update:open as the event-driven controlled value notification.
• Updates the composition example to return only the child output the parent needs.
• Docs-only change; release is intentionally deferred.

Verification

• pnpm -s cicheck