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/components/Newsletter.tsx

@@ -1,6 +1,21 @@
 import { Reveal } from "./Reveal";
 
-export function Newsletter() {
+type NewsletterProps = {
+  title?: string;
+  description?: string;
+};
+
+/**
+ * Reused as-is (same bordered/muted panel + icon-decoration + form
+ * pattern) on both Home and /newsletter (the "Impulse & Tipps" page) —
+ * their Figma frames use the exact same newsletter-inner component
+ * instance, just with different copy, so title/description are props
+ * instead of a second near-duplicate component.
+ */
+export function Newsletter({
+  title = "Starte mit einer Woche voller Klarheit",
+  description = "Melde dich zum Newsletter an und erhalte die 7-Tage-Challenge, mit der du durch mehr Struktur weniger Stress spürst.",
+}: NewsletterProps = {}) {
   return (
     <section className="py-16 w-full">
 
@@ -30,11 +45,10 @@ export function Newsletter() {
                 className="font-semibold text-h-section leading-normal"
                 style={{ fontFamily: "var(--font-lora)" }}
               >
-                Starte mit einer Woche voller Klarheit
+                {title}
               </p>
               <p className="font-normal text-body leading-6">
-                Melde dich zum Newsletter an und erhalte die 7-Tage-Challenge,
-                mit der du durch mehr Struktur weniger Stress spürst.
+                {description}
               </p>
             </div>
           </div>
@@ -52,7 +66,7 @@ export function Newsletter() {
                 />
                 <button
                   type="submit"
-                  className="shrink-0 bg-brand rounded-sm px-5 py-3 font-bold text-h4 text-text-primary tracking-[0.18px] whitespace-nowrap hover:brightness-95 active:scale-[0.97] transition-all"
+                  className="shrink-0 bg-brand rounded-sm px-5 py-3 font-bold text-h4 text-text-primary tracking-[0.18px] whitespace-nowrap hover:brightness-95 active:scale-[0.97] transition-all focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-brand focus-visible:ring-offset-2 focus-visible:ring-offset-bg-muted"
                 >
                   Jetzt anmelden
                 </button>