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]>

prisma/migrations/20261002120000_apicore_stock_sync/migration.sql

@@ -0,0 +1,63 @@
+-- Bestandsabgleich mit ApiCore (ApiCore/docs/superpowers/specs/2026-10-02-bestandsabgleich-design.md):
+-- ApiCore fuehrt den Restbestand je Charge; Wabenhain meldet bezahlte
+-- Verkaeufe und Rueckbuchungen ueber eine Warteschlange und gleicht seinen
+-- Shop-Bestand daran ab. Rein additiv.
+
+-- AlterEnum
+ALTER TYPE "ProductCategory" ADD VALUE 'SONSTIGES';
+
+-- CreateEnum
+CREATE TYPE "ApiCoreStockEventKind" AS ENUM ('SALE', 'RETURN');
+
+-- AlterTable
+ALTER TABLE "products" ADD COLUMN "apicoreProductId" TEXT;
+
+-- AlterTable
+ALTER TABLE "order_items" ADD COLUMN "apicoreAllocations" JSONB;
+
+-- CreateTable
+CREATE TABLE "apicore_stock_events" (
+    "id" TEXT NOT NULL,
+    "kind" "ApiCoreStockEventKind" NOT NULL,
+    "orderItemId" TEXT NOT NULL,
+    "productId" TEXT NOT NULL,
+    "apicoreBottlingId" TEXT,
+    "apicoreProductId" TEXT,
+    "quantity" INTEGER NOT NULL,
+    "reversesEventId" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "sentAt" TIMESTAMP(3),
+    "rejectedAt" TIMESTAMP(3),
+    "attempts" INTEGER NOT NULL DEFAULT 0,
+    "lastError" TEXT,
+    "nextAttemptAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "apicore_stock_events_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "products_apicoreProductId_key" ON "products"("apicoreProductId");
+
+-- CreateIndex
+CREATE INDEX "apicore_stock_events_sentAt_rejectedAt_nextAttemptAt_idx" ON "apicore_stock_events"("sentAt", "rejectedAt", "nextAttemptAt");
+
+-- CreateIndex
+CREATE INDEX "apicore_stock_events_orderItemId_idx" ON "apicore_stock_events"("orderItemId");
+
+-- CreateIndex
+CREATE INDEX "apicore_stock_events_productId_idx" ON "apicore_stock_events"("productId");
+
+-- AddForeignKey
+ALTER TABLE "apicore_stock_events" ADD CONSTRAINT "apicore_stock_events_orderItemId_fkey" FOREIGN KEY ("orderItemId") REFERENCES "order_items"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "apicore_stock_events" ADD CONSTRAINT "apicore_stock_events_productId_fkey" FOREIGN KEY ("productId") REFERENCES "products"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "apicore_stock_events" ADD CONSTRAINT "apicore_stock_events_reversesEventId_fkey" FOREIGN KEY ("reversesEventId") REFERENCES "apicore_stock_events"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
+
+-- Genau ein ApiCore-Ziel je Buchung.
+ALTER TABLE "apicore_stock_events" ADD CONSTRAINT "apicore_stock_events_exactly_one_target"
+  CHECK (("apicoreBottlingId" IS NULL) <> ("apicoreProductId" IS NULL));
+ALTER TABLE "apicore_stock_events" ADD CONSTRAINT "apicore_stock_events_quantity_positive"
+  CHECK ("quantity" > 0);