feat(frontend): due-overview card with start-review CTA

packages/frontend/src/components/DueOverviewCard.tsx

@@ -0,0 +1,55 @@
+import { useNavigate } from 'react-router-dom';
+import { sessionsApi } from '../api/sessions.js';
+import { useSession } from '../stores/sessionStore.js';
+
+export interface DueOverview { overdue: number; today: number; tomorrow: number; thisWeek: number; }
+
+export function DueOverviewCard({ data }: { data: DueOverview }) {
+  const navigate = useNavigate();
+  const total = data.overdue + data.today;
+  async function startReview() {
+    const r = await sessionsApi.startDue();
+    useSession.setState({
+      session: r.session,
+      current: r.queue[0] ?? null,
+      done: r.queue.length === 0,
+      showAnswer: false,
+      shownAt: Date.now(),
+    });
+    navigate(`/practice/${r.session.lessonId}`);
+  }
+
+  return (
+    <div className="surface space-y-4 p-5">
+      <div className="grid grid-cols-2 gap-3 sm:grid-cols-4">
+        <Badge tone="danger" label="Overdue" value={data.overdue} />
+        <Badge tone="brand" label="Vandaag" value={data.today} />
+        <Badge tone="success" label="Morgen" value={data.tomorrow} />
+        <Badge tone="muted" label="Deze week" value={data.thisWeek} />
+      </div>
+      <button
+        className="btn-primary w-full py-3"
+        onClick={startReview}
+        disabled={total === 0}
+      >
+        {total === 0
+          ? 'Niets te reviewen — alles up-to-date 🎉'
+          : `Start review (${total} ${total === 1 ? 'kaart' : 'kaarten'})`}
+      </button>
+    </div>
+  );
+}
+
+function Badge({ tone, label, value }: { tone: 'danger'|'brand'|'success'|'muted'; label: string; value: number }) {
+  const cls =
+    tone === 'danger' ? 'bg-danger-50 text-danger-700 dark:bg-danger-400/15 dark:text-danger-400'
+    : tone === 'brand' ? 'bg-brand-100 text-brand-700 dark:bg-brand-900/30 dark:text-brand-200'
+    : tone === 'success' ? 'bg-success-50 text-success-700 dark:bg-success-700/15 dark:text-success-400'
+    : 'bg-slate-100 text-slate-700 dark:bg-slate-800 dark:text-slate-300';
+  return (
+    <div className={`rounded-2xl p-3 ${cls}`}>
+      <div className="text-[10px] font-semibold uppercase tracking-wider opacity-80">{label}</div>
+      <div className="mt-1 font-display text-2xl font-bold">{value}</div>
+    </div>
+  );
+}