Waitlist pledges for node reservations

[denuoweb]

• Disabled paid node reservation checkout on NodePage.
• Reworked copy to “waitlist open / paid reservations paused.”
• Added waitlist form: name, email, intended quantity, required consent.
• Added POST /v1/node-reservation-pledges.
• Stores pledges in Firestore nodeReservationPledges, deduped by normalized email hash.
• Added validation and rate limiting.
• Updated legal/privacy copy for waitlist records and future reservation emails.
• Paused certification support payments in the UI.
• Kept existing Stripe checkout backend/API code intact for future re-enable.