Replace Unicode "←" with an SVG icon in cart's "Weiter einkaufen" links

Same font-fallback bug ArrowRightIcon.tsx already documents and fixed
for "→" elsewhere (Tools.tsx, Blog.tsx, ProductGrid.tsx) — the site's
custom web fonts don't cover U+2190, so it fell back to a system font
whose vertical metrics sit visibly low on mobile. Missed in that
earlier pass since CartContent.tsx uses the left-pointing twin.

app/cart/components/CartContent.tsx

@@ -13,6 +13,7 @@ import { formatPrice, discountPercent } from "../../lib/format";
 import { Reveal } from "../../components/Reveal";
 import { VersandModal } from "../../components/VersandModal";
 import { VatBreakdown } from "../../components/VatBreakdown";
+import { ArrowLeftIcon } from "../../components/ArrowLeftIcon";
 import { FreeShippingBanner } from "./FreeShippingBanner";
 import type { TrustBadge, ShippingSettings } from "../../lib/payload";
 
@@ -163,7 +164,7 @@ export function CartContent({
             href="/shop"
             className="flex gap-2 items-center text-text-primary hover:text-brand transition-colors"
           >
-            <span aria-hidden>←</span>
+            <ArrowLeftIcon />
             <span className="font-bold text-body-sm">Weiter einkaufen</span>
           </Link>
         </Reveal>