Add active-product-count-driven automation

- Products gain `active`/`spotlight*`/`updatedAt` on the base Product type
  (folded in from the now-removed separate SpotlightProduct type) so shop
  grid, spotlight, and related-products can each filter `.active` from the
  same already-fetched list — cart/checkout/order-confirmation/product-
  detail pages keep resolving any product regardless of active status.
- getSpotlightProduct() now derives from getProducts() instead of its own
  Payload query: with exactly 1 active product, that one IS the spotlight
  (overriding any `spotlight` flag elsewhere); otherwise same
  most-recently-updated tie-break as before, just computed client-side.
- ProductGrid drops the already-dead SHOP_GRID_EXCLUDE_IDS list in favor of
  the same `active` filter, with an empty-state message if 0 active.
- RelatedProducts gates on >=2 active products regardless of cart contents
  or how many display slots would otherwise resolve.
- Navbar's "Shop" link becomes an anchor to the homepage spotlight section
  (id="spotlight") instead of a real /shop navigation whenever exactly 1
  product is active — passed down from the now-async root layout, which
  fetches the catalog once for this decision.

app/cart/components/RelatedProducts.tsx

@@ -40,16 +40,20 @@ function pickWithFallback(allIds: string[], excludeIds: string[], keep: string[]
 export function RelatedProducts() {
   const cart = useCart();
   const products = useProducts();
+  // Cart/checkout resolve any product regardless of `active` (see
+  // Product's own comment in lib/payload.ts) — this is the one discovery
+  // surface among the useProducts() consumers, so it filters here itself.
+  const activeProducts = useMemo(() => products.filter((p) => p.active), [products]);
   const hasItems = cart.length > 0;
   const cartKey = cart
     .map((i) => i.id)
     .sort()
     .join(",");
   // useMemo, not a plain .map() — .map() would return a new array
-  // reference on every render regardless of whether `products` itself
+  // reference on every render regardless of whether `activeProducts` itself
   // changed, which would make the effect below re-run (and re-pick) every
   // single render if `productIds` were listed as its dependency.
-  const productIds = useMemo(() => products.map((p) => p.id), [products]);
+  const productIds = useMemo(() => activeProducts.map((p) => p.id), [activeProducts]);
 
   // Starts empty — the catalog itself is now fetched (useProducts()), so
   // there's nothing to pick a random set from until that resolves. The
@@ -94,10 +98,15 @@ export function RelatedProducts() {
   }, [cartKey, productIds]);
 
   const displayProducts = displayIds
-    .map((id) => products.find((p) => p.id === id))
+    .map((id) => activeProducts.find((p) => p.id === id))
     .filter((p): p is NonNullable<typeof p> => Boolean(p));
 
-  if (displayProducts.length === 0) return null;
+  // Section-wide gate, independent of cart contents or how many
+  // displayProducts happen to resolve: with only 1 active product,
+  // pickWithFallback's cart-item-reuse fallback could still populate a
+  // card, but a "related products" section makes no sense with fewer than
+  // 2 real alternatives to offer.
+  if (activeProducts.length < 2 || displayProducts.length === 0) return null;
 
   return (
     <section className="w-full bg-bg-base flex flex-col gap-8 items-center py-12 md:py-16 px-[var(--layout-padding-x)]">