Add shop, cart, versand pages and Impulse & Tipps detail page

- New /shop overview, /cart (real cart state via useSyncExternalStore),
  /versand (shipping policy page with TOC) and /newsletter detail page
- Cart: quantity/removal, order summary, related-products cross-sell
  with randomized picks, VersandModal quick-reference instead of
  navigating away, MwSt. disclosure next to unit prices
- Add-to-cart UX: inline success feedback (green state) plus a
  fly-to-navbar-cart-icon animation (CartFlyProvider) with a delayed
  badge count-up; AddToCartButton no longer navigates straight to /cart
- Shared lib/products.ts catalog and lib/shipping.ts constants (cost,
  free-shipping threshold, handling/transit days) so cart, trust badges
  and the versand page can never drift apart
- Fix Navbar smooth-scroll easing (ease-out instead of ease-in-out, no
  more perceived start delay); compress newsletter modal photo
  2.4MB -> 85KB to fix first-open jank

app/newsletter/page.tsx

@@ -0,0 +1,54 @@
+import type { Metadata } from "next";
+import { WeeklyImpulsesHero } from "./components/WeeklyImpulsesHero";
+import { HowItWorks } from "./components/HowItWorks";
+import { WeeklyBenefits } from "./components/WeeklyBenefits";
+import { Testimonials } from "./components/Testimonials";
+import { Newsletter } from "../components/Newsletter";
+import { Footer } from "../components/Footer";
+
+const title = "Impulse & Tipps – Wöchentliche Klarheit für deinen Alltag";
+const description =
+  "Einmal pro Woche bekommst du konkrete Impulse, die dich wirklich weiterbringen – kurz, praktisch und direkt umsetzbar. Kostenlos, jeden Mittwoch, jederzeit abbestellbar.";
+
+export const metadata: Metadata = {
+  title,
+  description,
+  alternates: {
+    canonical: "/newsletter",
+  },
+  openGraph: {
+    title,
+    description,
+    url: "/newsletter",
+    images: ["/hero-weekly-impulses.png"],
+  },
+  twitter: {
+    title,
+    description,
+    images: ["/hero-weekly-impulses.png"],
+  },
+};
+
+// Route is "/newsletter" — not "/impulse-tipps" or similar — because that
+// path already existed as a dangling link from two places (Navbar's
+// "Newsletter" CTA button and Tools.tsx's "Impulse & Tipps" → "Anmelden"
+// card). Both point at the same underlying thing (signing up for the
+// weekly newsletter), so this page resolves both at once instead of
+// picking a new URL and leaving one of them still dangling.
+export default function NewsletterPage() {
+  return (
+    <>
+      <main className="flex flex-col flex-1">
+        <WeeklyImpulsesHero />
+        <HowItWorks />
+        <WeeklyBenefits />
+        <Testimonials />
+        <Newsletter
+          title="Wöchentliche Impulse für mehr Klarheit"
+          description="Melde dich jetzt an und erhalte jeden Mittwoch neue Impulse & Tipps direkt in dein Postfach."
+        />
+      </main>
+      <Footer />
+    </>
+  );
+}