Simplify registration flow: mandatory signup redirect, payment emails, payment reminder cron

- EventRegistrationForm/WatcherForm/PerformerForm: remove session/login nudge/SuccessScreen;
  both roles redirect to /login?signup=1&email=<email>&next=/account after submit
- SuccessScreen.tsx deleted (no longer used)
- account.tsx: add 'Betaal nu' CTA via checkoutMutation (shown when watcher + paymentStatus pending)
- DB schema: add paymentReminderSentAt column to registration table
- Migration: 0008_payment_reminder_sent_at.sql
- email.ts: update registrationConfirmationHtml / sendConfirmationEmail with signupUrl param;
  add sendPaymentReminderEmail and sendPaymentConfirmationEmail functions
- routers/index.ts: wire payment reminder into runSendReminders() — queries watchers
  with paymentStatus pending, paymentReminderSentAt IS NULL, createdAt <= now-3days
- mollie.ts webhook: call sendPaymentConfirmationEmail after marking registration paid

apps/web/src/components/registration/PerformerForm.tsx

@@ -22,24 +22,13 @@ interface PerformerErrors {
 interface Props {
 	onBack: () => void;
 	onSuccess: (token: string, email: string, name: string) => void;
-	prefillFirstName?: string;
-	prefillLastName?: string;
-	prefillEmail?: string;
-	isLoggedIn?: boolean;
 }
 
-export function PerformerForm({
-	onBack,
-	onSuccess,
-	prefillFirstName = "",
-	prefillLastName = "",
-	prefillEmail = "",
-	isLoggedIn = false,
-}: Props) {
+export function PerformerForm({ onBack, onSuccess }: Props) {
 	const [data, setData] = useState({
-		firstName: prefillFirstName,
-		lastName: prefillLastName,
-		email: prefillEmail,
+		firstName: "",
+		lastName: "",
+		email: "",
 		phone: "",
 		artForm: "",
 		experience: "",
@@ -265,15 +254,14 @@ export function PerformerForm({
 							id="p-email"
 							name="email"
 							value={data.email}
-							onChange={isLoggedIn ? undefined : handleChange}
-							onBlur={isLoggedIn ? undefined : handleBlur}
-							readOnly={isLoggedIn}
+							onChange={handleChange}
+							onBlur={handleBlur}
 							placeholder="jouw@email.be"
 							autoComplete="email"
 							inputMode="email"
 							aria-required="true"
 							aria-invalid={touched.email && !!errors.email}
-							className={`${inputCls(!!touched.email && !!errors.email)}${isLoggedIn ? "cursor-not-allowed opacity-60" : ""}`}
+							className={inputCls(!!touched.email && !!errors.email)}
 						/>
 						{touched.email && errors.email && (
 							<span className="text-red-300 text-sm" role="alert">