New lib/newsEvents.ts registry (same pattern as newsSource.ts): OSS
default is a no-op sink; an extension overlay can register one to
forward the signals to its own analytics. NewsAnnouncer reports the
toast impression and modal opens (toast vs Help menu); NewsMarkdown
grows an optional onInteract callback fired on body link clicks and
YouTube preview plays — the admin authoring preview passes nothing, so
authoring never counts as engagement.
David Montero