Add wishlist feature (frontend), gated by CompanySettings.wishlistEnabled

New: useWishlist.ts (fetch+optimistic-toggle hook, server-backed since
a wishlist needs a logged-in customer, unlike the guest-friendly cart),
WishlistButton.tsx (heart toggle, login-redirects on 401), Navbar's
wishlist icon+badge (hidden below sm: — Account+Cart are the only
always-visible icons on true mobile, a 3rd icon there risks the same
computed nav-overflow class of bug documented in the figma-to-nextjs
skill), and /konto/merkliste (list page, 404s if the feature gets
disabled after a customer already has rows).

Product gained numericId (the raw Payload id) alongside its existing
slug id — WishlistItems.product is a real numeric relationship field,
unlike cart/checkout's slug-keyed "commerce id".

Backend counterpart (WishlistItems collection, CompanySettings toggle,
migration) already deployed separately.

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

app/api/account/wishlist/route.ts

@@ -0,0 +1,26 @@
+import { NextResponse } from "next/server";
+import { getSessionCustomer } from "../../../lib/customerAuth";
+import { getWishlist, toggleWishlistItem } from "../../../lib/customerAuth";
+
+export async function GET() {
+  const session = await getSessionCustomer();
+  if (!session) return NextResponse.json({ items: [] }, { status: 401 });
+  const items = await getWishlist(session.token, session.customer.id);
+  return NextResponse.json({ items });
+}
+
+export async function POST(request: Request) {
+  const session = await getSessionCustomer();
+  if (!session) return NextResponse.json({ ok: false, reason: "Bitte zuerst einloggen." }, { status: 401 });
+
+  const body = await request.json().catch(() => null);
+  const productId = Number(body?.productId);
+  const variant = typeof body?.variant === "string" ? body.variant : "";
+  if (!Number.isInteger(productId) || productId <= 0) {
+    return NextResponse.json({ ok: false, reason: "Ungültiges Produkt." }, { status: 400 });
+  }
+
+  const result = await toggleWishlistItem(session.token, 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 });
+}