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/routes/api/webhook/mollie.ts

@@ -1,4 +1,5 @@
 import { randomUUID } from "node:crypto";
+import { sendPaymentConfirmationEmail } from "@kk/api/email";
 import { creditRegistrationToAccount } from "@kk/api/routers/index";
 import { db } from "@kk/db";
 import { drinkkaart, drinkkaartTopup, registration } from "@kk/db/schema";
@@ -206,6 +207,20 @@ async function handleWebhook({ request }: { request: Request }) {
 			`Payment successful for registration ${registrationToken}, payment ${payment.id}`,
 		);
 
+		// Send payment confirmation email (fire-and-forget; don't block webhook)
+		sendPaymentConfirmationEmail({
+			to: regRow.email,
+			firstName: regRow.firstName,
+			managementToken: regRow.managementToken!,
+			drinkCardValue: regRow.drinkCardValue ?? undefined,
+			giftAmount: regRow.giftAmount ?? undefined,
+		}).catch((err) =>
+			console.error(
+				`Failed to send payment confirmation email for ${regRow.email}:`,
+				err,
+			),
+		);
+
 		// If this is a watcher with a drink card value, try to credit their
 		// drinkkaart immediately — but only if they already have an account.
 		if (