- Add REGISTRATION_OPENS_AT const in lib/opening.ts as single source of truth
- Add useRegistrationOpen hook with live 1s countdown ticker
- Add CountdownBanner component (DD/HH/MM/SS) with canvas-confetti on open
- EventRegistrationForm shows countdown instead of form while closed
- Login page hides/disables signup while closed; login always available
- WatcherForm AccountModal guards signUp call as defence-in-depth
Closes#2
