Add contract renewal reminder emails (keep/cancel decision links)

Sends a one-time email ~30 days before any contract's term_end
(whether renewal='auto' or 'none'), with "Behalten" and "Kündigen"
action links. "Behalten" extends the contract by one renewal term;
"Kündigen" sets the same cancellation effective-date logic as the
customer-facing cancel flow and opens a staff ticket so the external
deregistration (e.g. with a domain registrar) actually gets done.

Uses a dedicated single-use token table (contract_renewal_tokens)
since contracts, unlike user_tokens, are not scoped to a single user.
The public confirmation page lives at /vertrag-entscheidung.

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

apps/web/src/app/vertrag-entscheidung/page.tsx

@@ -0,0 +1,49 @@
+'use client';
+import { Suspense, useEffect, useState } from 'react';
+import { useSearchParams } from 'next/navigation';
+import { api, errMsg } from '@/lib/api';
+import { Alert } from '@/components/ui';
+
+interface Info { contractNumber: string; orgName: string; productName: string; termEnd: string }
+
+function Decision() {
+  const sp = useSearchParams();
+  const token = sp.get('token') ?? '';
+  const preselect = sp.get('action') === 'cancel' ? 'cancel' : sp.get('action') === 'keep' ? 'keep' : null;
+  const [info, setInfo] = useState<Info | null>(null);
+  const [err, setErr] = useState('');
+  const [busy, setBusy] = useState(false);
+  const [done, setDone] = useState<'keep' | 'cancel' | null>(null);
+
+  useEffect(() => {
+    if (!token) { setErr('Der Link ist unvollständig.'); return; }
+    api<Info>('GET', `/contracts/renewal-decision?token=${encodeURIComponent(token)}`).then(setInfo).catch((e) => setErr(errMsg(e)));
+  }, [token]);
+
+  async function decide(action: 'keep' | 'cancel') {
+    setBusy(true); setErr('');
+    try { await api('POST', '/contracts/renewal-decision', { token, action }); setDone(action); }
+    catch (e) { setErr(errMsg(e)); } finally { setBusy(false); }
+  }
+
+  return (<main id="main" className="center"><div className="auth card" style={{ maxWidth: 480 }}>
+    <h1>Vertragsentscheidung</h1>
+    {err && <Alert kind="err">{err}</Alert>}
+    {done ? (
+      <Alert kind="ok">
+        {done === 'keep' ? 'Vielen Dank! Der Vertrag wird weitergeführt.' : 'Die Kündigung wurde erfasst. Unser Team kümmert sich um die Abmeldung und meldet sich bei Rückfragen.'}
+      </Alert>
+    ) : info ? (<>
+      <p className="muted">
+        Vertrag <strong>{info.contractNumber}</strong> ({info.productName}) für <strong>{info.orgName}</strong> läuft am{' '}
+        <strong>{new Date(info.termEnd).toLocaleDateString('de-DE')}</strong> aus. Möchten Sie ihn behalten oder kündigen?
+      </p>
+      <div className="row" style={{ marginTop: 16 }}>
+        <button className="btn primary" disabled={busy} autoFocus={preselect === 'keep'} onClick={() => decide('keep')}>{busy ? '…' : 'Vertrag behalten'}</button>
+        <button className="btn danger" disabled={busy} autoFocus={preselect === 'cancel'} onClick={() => decide('cancel')}>{busy ? '…' : 'Vertrag kündigen'}</button>
+      </div>
+      <p className="muted small" style={{ marginTop: 16 }}>„Behalten" verlängert den Vertrag automatisch um eine weitere Laufzeit. „Kündigen" leitet die Abmeldung ein.</p>
+    </>) : !err && <p className="muted" role="status">Wird geladen …</p>}
+  </div></main>);
+}
+export default function Page() { return <Suspense><Decision /></Suspense>; }