feat(apicore-sync): field-level ownership between ApiCore and the shop

ApiCore stays the source of truth for beekeeping facts, Wabenhain for
everything sales-related; both remain separate packages talking only over
ApiCore's HTTP API.

- Batches: lot number, fill date, best-before date and filled jar count
  now follow ApiCore on every run (before: created once, corrections never
  arrived). remainingGlasses - the shop's own stock - is never written; if
  it exceeds a corrected fill quantity, the run reports it instead of
  silently adjusting.
- Batches are matched by the new Batch.apicoreBottlingId instead of the lot
  number, so correcting a lot number in ApiCore no longer creates a second
  batch. Existing synced batches are adopted once via their lot number.
- Harvests: date and year always follow ApiCore, also when published or
  edited; type, location and text stay as maintained in the admin.
- Products stay entirely shop-owned after creation (weight drives the
  legally required unit price, so it is never changed automatically).
- Admin panel: batch update count and stock-conflict notice; intro text
  states which system owns which fields.

Migration is additive (nullable unique column).

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

src/lib/apicore-mapping.test.ts

@@ -8,6 +8,8 @@ import {
   deriveJarWeightGrams,
   slugifyProductName,
   productSlugCandidates,
+  harvestFactChanges,
+  batchFactChanges,
 } from "./apicore-mapping";
 
 function makeProduct(overrides: Partial<ApiCoreProduct> = {}): ApiCoreProduct {
@@ -272,3 +274,70 @@ describe("isSellableStatus", () => {
     expect(isSellableStatus("")).toBe(false);
   });
 });
+
+describe("harvestFactChanges", () => {
+  test("liefert nichts, wenn Datum und Jahr unveraendert sind", () => {
+    // Arrange
+    const date = new Date("2026-07-14T00:00:00.000Z");
+
+    // Act
+    const changes = harvestFactChanges({ harvestDate: date, year: 2026 }, new Date(date));
+
+    // Assert
+    expect(changes).toEqual({});
+  });
+
+  test("uebernimmt ein in ApiCore korrigiertes Erntedatum samt Jahr", () => {
+    // Arrange
+    const existing = { harvestDate: new Date("2025-12-31T12:00:00.000Z"), year: 2025 };
+    const corrected = new Date("2026-01-02T12:00:00.000Z");
+
+    // Act
+    const changes = harvestFactChanges(existing, corrected);
+
+    // Assert
+    expect(changes).toEqual({ harvestDate: corrected, year: 2026 });
+  });
+});
+
+describe("batchFactChanges", () => {
+  const base = {
+    code: "WH-2026-0001",
+    fillDate: new Date("2026-08-01T00:00:00.000Z"),
+    bestBeforeDate: new Date("2028-08-01T00:00:00.000Z"),
+    glassCount: 100,
+  };
+
+  test("aktualisiert nur die ApiCore-eigenen Felder, die sich geaendert haben", () => {
+    // Arrange: MHD in ApiCore korrigiert, Shop hat 40 Glaeser verkauft.
+    const source = { ...base, bestBeforeDate: new Date("2028-07-31T00:00:00.000Z") };
+
+    // Act
+    const result = batchFactChanges({ ...base, remainingGlasses: 60 }, source);
+
+    // Assert
+    expect(result.changes).toEqual({ bestBeforeDate: source.bestBeforeDate });
+    expect(result.changes).not.toHaveProperty("remainingGlasses");
+    expect(result.stockExceedsFilled).toBe(false);
+  });
+
+  test("uebernimmt eine korrigierte Losnummer statt eine zweite Charge anzulegen", () => {
+    // Act
+    const result = batchFactChanges({ ...base, remainingGlasses: 100 }, { ...base, code: "WH-2026-0002" });
+
+    // Assert
+    expect(result.changes).toEqual({ code: "WH-2026-0002" });
+  });
+
+  test("meldet einen Shop-Bestand ueber der korrigierten Abfuellmenge, statt ihn anzugleichen", () => {
+    // Arrange: ApiCore korrigiert 100 auf 80 Glaeser, im Shop stehen noch 90.
+    const source = { ...base, glassCount: 80 };
+
+    // Act
+    const result = batchFactChanges({ ...base, remainingGlasses: 90 }, source);
+
+    // Assert
+    expect(result.changes).toEqual({ glassCount: 80 });
+    expect(result.stockExceedsFilled).toBe(true);
+  });
+});

src/lib/apicore-mapping.ts

@@ -135,3 +135,69 @@ export function productSlugCandidates(name: string, year: number, lotNumber: str
   const lot = slugifyProductName(lotNumber);
   return lot ? [withYear, `${withYear}-${lot}`] : [withYear];
 }
+
+// ---------------------------------------------------------------------------
+// Zustaendigkeit pro Feld
+// ---------------------------------------------------------------------------
+//
+// ApiCore ist die Quelle der Wahrheit fuer Imkerei-Fakten, Wabenhain fuer
+// alles, was den Verkauf betrifft. Die Funktionen unten liefern fuer einen
+// bereits vorhandenen Datensatz NUR die ApiCore-eigenen Felder, und nur
+// dann, wenn sie sich tatsaechlich geaendert haben. Alles andere (Texte,
+// Bilder, Preis, Sichtbarkeit, Shop-Bestand, Zuordnungen) bleibt unberuehrt —
+// auch dann, wenn ApiCore dort etwas anderes stehen haette.
+
+/** Ernte: Datum und Jahr sind Fakten aus ApiCore. */
+export interface HarvestFacts {
+  harvestDate: Date;
+  year: number;
+}
+
+export function harvestFactChanges(
+  existing: HarvestFacts,
+  sourceDate: Date
+): Partial<HarvestFacts> {
+  const changes: Partial<HarvestFacts> = {};
+  if (existing.harvestDate.getTime() !== sourceDate.getTime()) changes.harvestDate = sourceDate;
+  const year = sourceDate.getFullYear();
+  if (existing.year !== year) changes.year = year;
+  return changes;
+}
+
+/**
+ * Charge: Losnummer, Abfuelldatum, Mindesthaltbarkeit und abgefuellte
+ * Glasanzahl sind Fakten aus ApiCore. `remainingGlasses` ist dagegen
+ * Wabenhains Shop-Bestand, veraendert durch echte Verkaeufe, und wird nie
+ * gesetzt.
+ */
+export interface BatchFacts {
+  code: string;
+  fillDate: Date;
+  bestBeforeDate: Date;
+  glassCount: number;
+}
+
+export interface BatchFactUpdate {
+  changes: Partial<BatchFacts>;
+  /**
+   * Der Shop-Bestand liegt nach der Korrektur ueber der abgefuellten Menge —
+   * das kann nur ein Mensch aufloesen (Zaehlfehler hier oder dort?), also
+   * wird es gemeldet statt still angeglichen.
+   */
+  stockExceedsFilled: boolean;
+}
+
+export function batchFactChanges(
+  existing: BatchFacts & { remainingGlasses: number },
+  source: BatchFacts
+): BatchFactUpdate {
+  const changes: Partial<BatchFacts> = {};
+  if (existing.code !== source.code) changes.code = source.code;
+  if (existing.fillDate.getTime() !== source.fillDate.getTime()) changes.fillDate = source.fillDate;
+  if (existing.bestBeforeDate.getTime() !== source.bestBeforeDate.getTime()) {
+    changes.bestBeforeDate = source.bestBeforeDate;
+  }
+  if (existing.glassCount !== source.glassCount) changes.glassCount = source.glassCount;
+  const glassCount = changes.glassCount ?? existing.glassCount;
+  return { changes, stockExceedsFilled: existing.remainingGlasses > glassCount };
+}