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

public/pagination-dots.svg

@@ -0,0 +1,13 @@
+<svg preserveAspectRatio="none" width="100%" height="100%" overflow="visible" style="display: block;" viewBox="0 0 56 8" fill="none" xmlns="http://www.w3.org/2000/svg">
+<g id="pagination-dots" clip-path="url(#clip0_0_68)">
+<circle id="dot" cx="4" cy="4" r="4" fill="var(--fill-0, #F6A701)"/>
+<circle id="dot_2" cx="20" cy="4" r="4" fill="var(--fill-0, #D9D9D9)"/>
+<circle id="dot_3" cx="36" cy="4" r="4" fill="var(--fill-0, #D9D9D9)"/>
+<circle id="dot_4" cx="52" cy="4" r="4" fill="var(--fill-0, #D9D9D9)"/>
+</g>
+<defs>
+<clipPath id="clip0_0_68">
+<rect width="56" height="8" fill="white"/>
+</clipPath>
+</defs>
+</svg>