Send activation link immediately for walk-in and manual registration accounts

Accounts created by staff on someone's behalf now get their activation
link (email or WhatsApp) sent right away, instead of only on a first
failed login attempt, matching what the Terms of Use already promised.
This also fixed a real account with a real email being silently
activated with a fixed, undisclosed password (Hope123).

Also fixes the self-service kiosk's "Create an account" password field,
which never actually took effect server-side, and removes the "Guest
(no account)" checkboxes that no longer had any backend effect once
every walk-in account started behaving the same way.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/dashboard/supervisor/at-the-door/page.tsx

@@ -242,7 +242,6 @@ export default function AtTheDoorPage() {
                     authToken: token,
                     body: {
                         eventId,
-                        guestOnly: pendingUser.guestOnly,
                         user: {
                             name: pendingUser.name,
                             ...(pendingUser.email ? { email: pendingUser.email } : {}),
@@ -282,7 +281,7 @@ export default function AtTheDoorPage() {
         });
         setQuantities(qtyMap);
         setMinQuantities({});
-        setPendingUser({ guestOnly: true, name, email: email || null, phone: phone || null, notifPref });
+        setPendingUser({ name, email: email || null, phone: phone || null, notifPref });
         setPendingEditReg(null);
         setShowNewAttendeeModal(false);
         setShowOptionsModal(true);