Fix wishlist items not saving: pass customerId into toggleWishlistItem

The create POST omitted the customer relationship field entirely, so
added items never matched getWishlist's customer-scoped query. Also
scope the toggle-off fallback lookup to the current customer.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/api/account/wishlist/route.ts

@@ -20,7 +20,7 @@ export async function POST(request: Request) {
     return NextResponse.json({ ok: false, reason: "Ungültiges Produkt." }, { status: 400 });
   }
 
-  const result = await toggleWishlistItem(session.token, productId, variant);
+  const result = await toggleWishlistItem(session.token, session.customer.id, productId, variant);
   if (!result.ok) return NextResponse.json({ ok: false, reason: "Merkliste konnte nicht aktualisiert werden." }, { status: 500 });
   return NextResponse.json({ ok: true, wishlisted: result.wishlisted });
 }

app/lib/customerAuth.ts

@@ -435,17 +435,19 @@ export async function getWishlist(token: string, customerId: number): Promise<Wi
 // toggle (the common case, adding something new, only needs one request).
 export async function toggleWishlistItem(
   token: string,
+  customerId: number,
   productId: number,
   variant: string,
 ): Promise<{ ok: true; wishlisted: boolean } | { ok: false }> {
   const createRes = await fetch(`${PAYLOAD_URL}/api/wishlist-items`, {
     method: "POST",
     headers: { Authorization: `JWT ${token}`, "Content-Type": "application/json" },
-    body: JSON.stringify({ product: productId, variant }),
+    body: JSON.stringify({ customer: customerId, product: productId, variant }),
   });
   if (createRes.ok) return { ok: true, wishlisted: true };
 
   const findParams = new URLSearchParams({
+    "where[customer][equals]": String(customerId),
     "where[product][equals]": String(productId),
     "where[variant][equals]": variant,
     depth: "0",