In-app announcement badges via widget

Close the changelog loop inside customers own products. The existing widget can show a small What is new badge when new changelog entries are published. Users can open a compact announcement panel, mark entries as seen, and click through to the full changelog.

Requires per-visitor seen state (anonymous cookie + optional signed user id), widget configuration for badge placement/theme, and changelog publish hook. Strong value prop: teams can notify active users without relying only on email.