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/retouren/actions.ts

@@ -9,6 +9,8 @@ import { logAdminAction } from "@/lib/audit-log";
 import { sendMail } from "@/lib/mail";
 import { returnAcceptedEmail, returnRejectedEmail, returnRefundedEmail } from "@/lib/email-templates";
 import { restockOrderItems } from "@/lib/inventory";
+import { recordOrderReturn } from "@/lib/apicore-stock/stock-events";
+import { scheduleApiCoreStockSync } from "@/lib/apicore-stock/schedule";
 import { isLocale, defaultLocale } from "@/i18n/config";
 
 function str(formData: FormData, key: string): string {
@@ -114,7 +116,11 @@ export async function refundReturnRequestAction(formData: FormData): Promise<voi
     // Zurueckgesendete Ware wieder als verfuegbaren Bestand fuehren, analog
     // zur Stornierung im Checkout-Webhook.
     await restockOrderItems(tx, returnRequest.order.items);
+    // Die zurueckgesendete Ware geht auch in ApiCore zurueck auf die
+    // Chargen, aus denen sie verkauft wurde.
+    await recordOrderReturn(tx, returnRequest.orderId);
   });
+  scheduleApiCoreStockSync(returnRequest.order.items.map((item) => item.productId));
 
   await logAdminAction(admin, {
     action: "return_request.refund",