Pages can point at the chat

Course lessons keep telling newcomers that the chat is "always one click away in the top menu" — and until now the page had no way to show them. A page can now link its own URL with ?hint=chat: landing on such a link makes the header's chat toggle pulse gently for a few seconds, so the eye finds it. Nothing else happens — no navigation, no panel opening — and clicking the toggle (or just waiting) ends the pulse.