Fix more mobile responsive issues: Hero, arrows, cart button, checkmarks, modal

- Newsletter card icon: fixed an aspect-ratio distortion bug (w-16 maps
  to this project's fluid --spacing-16, which floors to 40px below
  768px, paired with a fixed 55px height — squished the icon on
  mobile). Same root cause existed in NewsletterModal's envelope icon;
  that one's now just hidden below md: instead per feedback.
- Hero: subtitle sized down and CTA checkmark icon scaled to match
  below lg:, social proof text always wraps below the avatars there
  instead of only when it doesn't fit.
- Werkzeuge connector arrows (todo-cards/newsletter/challenge
  HowItWorks): object-contain added — the SVG has
  preserveAspectRatio="none" and was stretching to fill the square
  mobile box instead of keeping its thin-arrow shape.
- Challenge bottom CTA: icon now stacks above the copy, centered, below
  lg: to match the Home Newsletter card's pattern.
- Homepage Werkzeuge icons: smaller below md: to match the (fluid-floor)
  text size next to them.
- Blog detail "Passend dazu" card: the fixed w-[19rem] title column plus
  "Entdecken" sharing its row overflowed on mobile; stacked below sm:
  instead, with a little top margin on "Entdecken".
- Todo-Karten checklist checkmarks: recolored brand-orange (icon-check
  .svg's fill lives in an internal CSS var that can't be overridden from
  outside an <img>-loaded SVG, so switched to an inline SVG) and
  top-aligned instead of vertically centered.
- AddToCartButton: added whitespace-nowrap to the stacked-label grid
  (used to reserve button width across all possible label texts) — one
  of those labels wrapping to two lines on a narrow w-full button was
  inflating the row height for whichever label is actually showing,
  leaving a tall empty gap under "Ausverkauft".

app/components/Tools.tsx

@@ -38,9 +38,13 @@ export async function Tools() {
             key={tool.id}
             className="md:col-span-4 flex gap-8 items-start rounded-md transition-transform duration-300 hover:-translate-y-1"
           >
-            {/* Icon — uniform box, pre-flipped/rotated source asset */}
-            <div className="relative flex items-center justify-center shrink-0 size-14">
-              <Image alt="" src={tool.icon} fill sizes="56px" className="object-contain" />
+            {/* Icon — uniform box, pre-flipped/rotated source asset.
+                size-14 (56px) is a fixed value at every width (14 isn't
+                one of this project's fluid spacing-scale steps) — smaller
+                below md: so it doesn't dwarf the title/description text,
+                which does shrink toward its own fluid floor there. */}
+            <div className="relative flex items-center justify-center shrink-0 size-11 md:size-14">
+              <Image alt="" src={tool.icon} fill sizes="(min-width: 768px) 56px, 44px" className="object-contain" />
             </div>
 
             {/* Card content — self-stretch + h-full + justify-between so