Fix several mobile responsive issues across Hero, Newsletter, cart, and Challenge

- Hero CTA: back to a single line below lg: (wrapping put the icon
  beside two lines and looked broken), sized down instead so the full
  phrase fits.
- Hero heading: dropped the forced <br> after "darf" at true mobile
  widths, kept it only for the sm-lg tablet range it was added for.
- Hero social proof: avatars+text now wrap and center instead of
  cramming onto one row (flex-wrap + justify-center, no fixed
  breakpoint needed).
- Newsletter card icon: stacked above the copy and centered below md:
  instead of squeezed into a row beside it.
- TrustRow: left-aligned below md: instead of centered (shop, cart, and
  every other page using this component).
- Cart line item image: full width below sm: instead of a fixed 150px
  square.
- Challenge EmailCapture (top + bottom CTA, same shared component):
  input and button stack full-width below sm: instead of squeezing
  into one row.
- Challenge steps: icon above text and centered at every breakpoint
  (previously only from lg: up), connector arrows centered to match.

app/challenge/page.tsx

@@ -231,13 +231,21 @@ export default async function ChallengePage() {
               <p className="text-[1rem] text-[#666]">Jeden Tag ein Impuls. In nur wenigen Minuten.</p>
             </Reveal>
 
-            <RevealGroup className="flex flex-col lg:flex-row items-start lg:items-start gap-8 lg:gap-2 w-full">
+            {/* items-center below lg: (was items-start) — the step blocks
+                are centered columns now (see RevealItem below), so the
+                connector arrows between them need to be centered too,
+                not flush against the left edge. */}
+            <RevealGroup className="flex flex-col lg:flex-row items-center lg:items-start gap-8 lg:gap-2 w-full">
               {steps.flatMap((step, i) => [
-                <RevealItem key={step.title} className="group flex lg:flex-col items-start lg:items-center gap-4 lg:gap-5 flex-1 min-w-0">
+                // Icon-above-text, centered, at every breakpoint now
+                // (previously a left-aligned icon+text row below lg: —
+                // fixed 2026-07-24 to match the lg: layout instead of
+                // diverging from it).
+                <RevealItem key={step.title} className="group flex flex-col items-center gap-4 lg:gap-5 flex-1 min-w-0">
                   <div className="flex items-center justify-center w-16 h-14 shrink-0 transition-transform duration-300 group-hover:scale-110">
                     {step.icon}
                   </div>
-                  <div className="flex flex-col gap-1 lg:text-center">
+                  <div className="flex flex-col gap-1 text-center">
                     <p className="font-semibold text-[#222221] text-[1rem]">{step.title}</p>
                     <p className="text-[0.875rem] text-[#666] leading-[1.5]">{step.desc}</p>
                   </div>