Add product image gallery, harden Klaro border reset, remove attribution link

ProductGallery.tsx (main image + thumbnail strip) wired into
TodoKartenHero.tsx, only replacing the static hero photo once a
product actually has extra gallery photos — no visual change
otherwise. Backend field: Products.gallery (see payload repo).

Klaro's hard black border was still showing after the previous
color-only pass — the targeted border:none rule wasn't enough, so
this blanket-resets border/outline on every .klaro descendant and
re-adds only the shadow this theme actually wants. Also disables the
"Realisiert mit Klaro!" attribution link (BSD-3-Clause has no
on-page-attribution requirement, Klaro's own disablePoweredBy flag
covers this cleanly).

Updates the frontend README with the gallery + Klaro fixes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -1854,6 +1854,26 @@ has its own dedicated Live Preview renderer, not the shared generic
 order-status one — there's no order for this email type, so no fake
 "Bestellnummer" line; CTA is "Zum Produkt", not "Bestellung ansehen".
 
+## Product image gallery
+
+`ProductGallery.tsx` — main image + thumbnail strip, swappable on click,
+backed by an optional `Products.gallery` field (backend, `hasMany` upload,
+empty for most products — see the Payload README). Renders as a single
+plain image with no thumbnail row at all when `gallery` is empty, i.e. the
+same appearance every product already had before this existed — a product
+only gets the gallery UI once someone deliberately adds extra photos in
+the admin.
+
+There's no generic `/shop/[slug]` product detail page in this app — every
+product beyond the plain grid card gets a bespoke hero page (currently
+just `/todo-cards`), matching the custom-per-client site model.
+`ProductGallery` is wired into `TodoKartenHero.tsx` as a drop-in
+replacement for that page's static hero photo — but only once
+`product.gallery.length > 0`; otherwise the curated static lifestyle
+photo (`/hero-todo-karten.png`, deliberately not just the catalog image)
+stays exactly as it was. A future bespoke product page can reuse the same
+component the same way.
+
 ## Tests
 
 `npm run test:unit` (Vitest, `node` environment, no jsdom/Next.js runtime