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/components/Navbar.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useMemo, useRef, useState } from "react";
 import Link from "next/link";
 import Image from "next/image";
 import { usePathname } from "next/navigation";
@@ -31,16 +31,21 @@ function smoothScrollTo(targetY: number) {
   requestAnimationFrame(step);
 }
 
-const navLinks = [
-  { label: "Werkzeuge", href: "#werkzeuge" },
-  { label: "Blog", href: "/blog" },
-  { label: "Über Björn", href: "#ueber-bjoern" },
-  { label: "Shop", href: "/shop" },
-];
-
-const anchorIds = navLinks
-  .filter((l) => l.href.startsWith("#"))
-  .map((l) => l.href.slice(1));
+// "Shop" becomes an in-page anchor to the homepage's ProductSpotlight
+// section (id="spotlight") instead of a real /shop navigation whenever
+// exactly 1 product is active — same reasoning as the other anchor links,
+// #werkzeuge/#ueber-bjoern already have (a full catalog grid is
+// degenerate UX with only 1 item to show). Passed down from
+// app/layout.tsx, which is the one place already fetching the product
+// catalog for this decision.
+function getNavLinks(singleActiveProduct: boolean) {
+  return [
+    { label: "Werkzeuge", href: "#werkzeuge" },
+    { label: "Blog", href: "/blog" },
+    { label: "Über Björn", href: "#ueber-bjoern" },
+    { label: "Shop", href: singleActiveProduct ? "#spotlight" : "/shop" },
+  ];
+}
 
 // "Werkzeuge" also covers standalone tool/product pages that live under
 // the Home "Werkzeuge" section conceptually — /todo-cards (ToDo-Karten),
@@ -145,7 +150,7 @@ function CartLink() {
   );
 }
 
-export function Navbar() {
+export function Navbar({ singleActiveProduct }: { singleActiveProduct: boolean }) {
   const pathname = usePathname();
   const [scrolled, setScrolled] = useState(false);
   const [activeSection, setActiveSection] = useState("");
@@ -154,6 +159,12 @@ export function Navbar() {
   const panelRef = useRef<HTMLDivElement>(null);
   const hamburgerRef = useRef<HTMLButtonElement>(null);
 
+  const navLinks = useMemo(() => getNavLinks(singleActiveProduct), [singleActiveProduct]);
+  const anchorIds = useMemo(
+    () => navLinks.filter((l) => l.href.startsWith("#")).map((l) => l.href.slice(1)),
+    [navLinks]
+  );
+
   useEffect(() => {
     const onScroll = () => setScrolled(window.scrollY > 8);
     window.addEventListener("scroll", onScroll, { passive: true });
@@ -197,7 +208,7 @@ export function Navbar() {
       }
     }, 50);
     return () => clearTimeout(timer);
-  }, [pathname]);
+  }, [pathname, anchorIds]);
 
   useEffect(() => {
     const onScroll = () => {
@@ -216,7 +227,7 @@ export function Navbar() {
     onScroll();
     window.addEventListener("scroll", onScroll, { passive: true });
     return () => window.removeEventListener("scroll", onScroll);
-  }, []);
+  }, [anchorIds]);
 
   // Close on viewport resize past the structural breakpoint, so the drawer
   // never lingers open behind the (now visible) desktop nav. The hamburger