feat(stock): keep shop stock in sync with ApiCore, write sales back

ApiCore now owns the remaining stock per batch; the shop sells from it
and reports every paid sale and every return back.

- Outbox apicore_stock_events, written in the same transaction as the
  status change: paid -> SALE, cancelled-after-payment / refunded return
  -> RETURN onto the batches of the sale, reopened paid order -> SALE.
  Whether a return is due is decided by the open sales in the outbox,
  so unpaid orders never book and nothing is booked twice.
- Delivery right after the response (next/server after()) plus CronJob
  wabenhain-apicore-stock every 10 minutes with 1/5/15/60 min backoff;
  ApiCore deduplicates by event id. Rejected bookings stop and show up
  on the dashboard.
- Reconcile: shop stock = ApiCore remaining - unconfirmed bookings -
  reservations of unpaid orders, in a serializable transaction like the
  checkout. Triggered after bookings, by the signed ApiCore webhook
  stock.changed (ids only, numbers are fetched) and by the sync button.
- Manufactured goods (candles, propolis products, ...): one shop product
  per ApiCore article via Product.apicoreProductId, drafts created by the
  sync, existing products linkable in the product form; new category
  SONSTIGES. Stock field is read-only for linked products.
- OrderItem.apicoreAllocations keeps which lots were sold (recalls).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

src/app/admin/page.tsx

@@ -2,6 +2,7 @@ import Link from "next/link";
 import { ApiCoreSyncPanel, ApiCoreSyncResult } from "@/components/apicore-sync-panel";
 import { prisma } from "@/lib/prisma";
 import { pendingReviewWhere } from "@/lib/review-status";
+import { countApiCoreStockIssues } from "@/lib/apicore-stock/dashboard";
 import { COUNTED_SALE_WHERE } from "@/lib/sales";
 import { formatPrice } from "@/lib/format";
 import { getLocale } from "@/i18n/locale";
@@ -259,6 +260,12 @@ export default async function AdminDashboardPage(props: PageProps<"/admin">) {
   const revenueTrend = [...revenueByDay.entries()];
   const maxDailyRevenue = Math.max(1, ...revenueTrend.map(([, v]) => v));
 
+  // Bestandsabgleich mit ApiCore (nur wenn eingerichtet).
+  const stockIssues = await countApiCoreStockIssues();
+  const stockOverdue = stockIssues.overdue;
+  const stockRejected = stockIssues.rejected;
+  const unlinkedProducts = stockIssues.unlinked;
+
   const [admin, waitingOrders, waitingReturns, waitingReviews, waitingInquiries] = await Promise.all([
     getCurrentAdmin(),
     prisma.order.count({
@@ -273,6 +280,9 @@ export default async function AdminDashboardPage(props: PageProps<"/admin">) {
     { count: waitingReturns, href: "/admin/retouren", label: t.adminDashboardPage.toDoReturns(waitingReturns) },
     { count: waitingReviews, href: "/admin/bewertungen", label: t.adminDashboardPage.toDoReviews(waitingReviews) },
     { count: waitingInquiries, href: "/admin/anfragen", label: t.adminDashboardPage.toDoInquiries(waitingInquiries) },
+    { count: stockRejected, href: "/admin/bestellungen", label: t.adminDashboardPage.toDoStockRejected(stockRejected) },
+    { count: stockOverdue, href: "/admin", label: t.adminDashboardPage.toDoStockOverdue(stockOverdue) },
+    { count: unlinkedProducts, href: "/admin/produkte", label: t.adminDashboardPage.toDoUnlinkedProducts(unlinkedProducts) },
   ].filter((item) => item.count > 0);
 
   // Begruessung nach Tageszeit in Berliner Zeit (der Server laeuft in UTC).