feat(newsletter, checkout): add consent links, unify trust-note styling, optimize images

Every email-signup form (Home/newsletter Newsletter section, /newsletter
hero, /challenge, the Newsletter overlay) now links "Datenschutzerklärung"
to /datenschutz next to its consent checkbox, opened in a new tab so a
partially filled form isn't lost. Checkout gets an equivalent AGB +
Datenschutzerklärung note under the order button, and the Versand
modal's Widerrufsbelehrung link also opens in a new tab.

Unified the "Keine Werbung. Jederzeit abbestellbar." trust note (icon +
#888 copy) across all newsletter forms, matching /challenge's existing
style instead of each form having its own wording/color.

Also converted the remaining raw <img> tags in these files to next/image
per the no-img-element lint rule (bandwidth/LCP).

app/versand/components/VersandSections.tsx

@@ -102,7 +102,7 @@ export function VersandSections({ withAnchors = false }: { withAnchors?: boolean
         <p>
           Informationen zu Rückgabe, Rücksendekosten und deinem gesetzlichen Widerrufsrecht findest
           du in unserer{" "}
-          <Link href="/widerruf" className="text-brand hover:underline">
+          <Link href="/widerruf" target="_blank" rel="noopener noreferrer" className="text-brand hover:underline">
             Widerrufsbelehrung
           </Link>
           .