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/content/help/supervisor-manual.tsx

@@ -14,7 +14,7 @@ export const supervisorManualHelpContent: HelpContent = {
       icon: UserPlus,
       content: (
         <div className="space-y-4">
-          <p>Pick an event, then either search for an existing user or enter guest details (name, email, phone) and tick &quot;Guest&quot; to skip linking an account. Choose ticket options and quantities — early-bird pricing is applied automatically — then create the registration.</p>
+          <p>Pick an event, then either search for an existing user or enter guest details (name, and at least one of email or phone). Choose ticket options and quantities — early-bird pricing is applied automatically — then create the registration. A new guest account is created inactive, and an activation link is sent immediately (by email if provided, otherwise WhatsApp) so they can set their own password.</p>
           <p className="text-xs text-gray-500">After creating a registration, the Record Payment tab is pre-filled with it — switch tabs to take payment right away.</p>
         </div>
       ),