feat(sponsor): show Stripe wordmark above the one-time/monthly toggle

Adds a subtle "payments processed by Stripe" indicator (official
wordmark SVG from Simple Icons, muted/low-opacity) above the
contribution-type selector on the Unterstützen page, so visitors know
which payment provider handles the transaction before choosing an
option.

messages/de.json

@@ -137,6 +137,7 @@
   "Sponsor": {
     "title": "PawFeed unterstützen",
     "subtitle": "PawFeed wird komplett privat finanziert — ganz ohne Investoren, aus eigener Tasche. Server-Hardware, Software-Lizenzen und weitere Tools verursachen laufende Kosten. Mit deinem freiwilligen Beitrag hilfst du, die Plattform am Laufen zu halten — als Dankeschön bekommst du das Sponsor-Badge auf deinem Profil und bei jedem Beitrag.",
+    "poweredByStripe": "Zahlungsabwicklung über",
     "oneTime": "Einmalig",
     "monthly": "Monatlich",
     "customAmountLabel": "Betrag in Euro",

messages/en.json

@@ -137,6 +137,7 @@
   "Sponsor": {
     "title": "Support PawFeed",
     "subtitle": "PawFeed is entirely privately financed — no investors, out of pocket. Server hardware, software licenses, and other tools mean ongoing costs. Your voluntary contribution helps keep the platform running — as a thank-you, you get the Sponsor badge on your profile and on every post.",
+    "poweredByStripe": "Payments processed by",
     "oneTime": "One-time",
     "monthly": "Monthly",
     "customAmountLabel": "Amount in Euro",

src/app/(app)/unterstuetzen/page.tsx

@@ -97,6 +97,18 @@ export default function SponsorPage() {
       )}
 
       <div className="rounded-2xl border border-border bg-card p-6">
+        <div className="mb-4 flex items-center justify-center gap-1.5 text-muted-foreground/40">
+          <span className="text-xs">{t("poweredByStripe")}</span>
+          <svg
+            viewBox="0 0 24 24"
+            className="h-4 w-4"
+            fill="currentColor"
+            aria-hidden="true"
+          >
+            <path d="M13.976 9.15c-2.172-.806-3.356-1.426-3.356-2.409 0-.831.683-1.305 1.901-1.305 2.227 0 4.515.858 6.09 1.631l.89-5.494C18.252.975 15.697 0 12.165 0 9.667 0 7.589.654 6.104 1.872 4.56 3.147 3.757 4.992 3.757 7.218c0 4.039 2.467 5.76 6.476 7.219 2.585.92 3.445 1.574 3.445 2.583 0 .98-.84 1.545-2.354 1.545-1.875 0-4.965-.921-6.99-2.109l-.9 5.555C5.175 22.99 8.385 24 11.714 24c2.641 0 4.843-.624 6.328-1.813 1.664-1.305 2.525-3.236 2.525-5.732 0-4.128-2.524-5.851-6.594-7.305h.003z" />
+          </svg>
+        </div>
+
         <div className="mb-5 flex gap-2">
           {(["ONE_TIME", "SUBSCRIPTION"] as const).map((option) => (
             <button