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/lib/apicore-stock/dashboard.ts

@@ -0,0 +1,28 @@
+import { prisma } from "@/lib/prisma";
+import { OVERDUE_AFTER_MS } from "./stock-math";
+
+export interface ApiCoreStockIssues {
+  /** Seit ueber 15 Minuten nicht bei ApiCore angekommen. */
+  overdue: number;
+  /** Von ApiCore abgelehnt — braucht einen Menschen. */
+  rejected: number;
+  /** Aktive Produkte, deren Bestand noch von Hand gepflegt wird. */
+  unlinked: number;
+}
+
+/**
+ * Stoerungen des Bestandsabgleichs fuer das Admin-Dashboard. Ohne
+ * ApiCore-Konfiguration gibt es nichts zu melden.
+ */
+export async function countApiCoreStockIssues(now: Date = new Date()): Promise<ApiCoreStockIssues> {
+  const configured = Boolean(process.env.APICORE_API_URL?.trim() && process.env.APICORE_API_KEY?.trim());
+  if (!configured) return { overdue: 0, rejected: 0, unlinked: 0 };
+  const [overdue, rejected, unlinked] = await Promise.all([
+    prisma.apiCoreStockEvent.count({
+      where: { sentAt: null, rejectedAt: null, createdAt: { lt: new Date(now.getTime() - OVERDUE_AFTER_MS) } },
+    }),
+    prisma.apiCoreStockEvent.count({ where: { rejectedAt: { not: null } } }),
+    prisma.product.count({ where: { isActive: true, apicoreBottlingId: null, apicoreProductId: null } }),
+  ]);
+  return { overdue, rejected, unlinked };
+}