feat: add 30-day money back guarantee trust badge above complete order button

- Add green trust badge with checkmark icon above 'Complete Order' button
- Add translations for all locales (EN, SR, DE, FR)
- Badge includes: '30-Day Money-Back Guarantee' text
- Styled with green background and border to match trust/conversion theme

src/i18n/messages/de.json

@@ -361,6 +361,7 @@
     "cashOnDeliveryDesc": "Bezahlen Sie, wenn Ihre Bestellung an Ihre Tür geliefert wird.",
     "processing": "Wird bearbeitet...",
     "completeOrder": "Bestellung abschließen - {total}",
+    "moneyBackGuarantee": "30 Tage Geld-zurück-Garantie",
     "orderSummary": "Bestellübersicht",
     "qty": "Menge",
     "subtotal": "Zwischensumme",