Add rate limiting, sliding sessions, email verification, GDPR self-service, order cancellation/returns, and critical-error alerting

Complements Payload's per-account login lockout with per-IP rate limiting
on auth routes; proxy.ts silently refreshes an active customer's session
via Payload's built-in refresh-token endpoint instead of a long-lived
token. Registration now sends a non-blocking email-verification link
(doesn't gate login, since checkout registers and immediately logs in
mid-purchase). /konto/profil gets GDPR export/delete; order detail pages
get self-service cancel/return-request, backed by a Payload hook that
closes a real gap (a customer's JWT could previously PATCH any field of
their own order, not just status). Checkout failures now email an alert
independent of Payload's own health, since Kuma's uptime checks can't see
an order silently failing to persist.

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

app/api/health/route.ts

@@ -0,0 +1,21 @@
+import { NextResponse } from "next/server";
+
+const PAYLOAD_URL = process.env.PAYLOAD_URL || "https://payload.mk360.de";
+
+// Deliberately checks Payload connectivity, not just "did this route
+// handler run" — the site can return 200s from every static/ISR page
+// while Payload itself is unreachable (stale cached content masks it for
+// a while). Meant for a Kuma HTTP monitor, added to the existing "Content
+// & API" group alongside the direct Payload monitors (see ~/dev/README.md).
+export async function GET() {
+  try {
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), 3000);
+    const res = await fetch(`${PAYLOAD_URL}/api/posts?limit=1`, { signal: controller.signal, cache: "no-store" });
+    clearTimeout(timeout);
+    if (!res.ok) return NextResponse.json({ ok: false, payload: false }, { status: 503 });
+    return NextResponse.json({ ok: true });
+  } catch {
+    return NextResponse.json({ ok: false, payload: false }, { status: 503 });
+  }
+}