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/app/[locale]/checkout/page.tsx

@@ -709,6 +709,14 @@ export default function CheckoutPage() {
                     disabled={isLoading}
                   />
 
+                  {/* Money Back Guarantee Trust Badge */}
+                  <div className="flex items-center justify-center gap-2 py-3 px-4 bg-green-50 rounded-lg border border-green-100">
+                    <svg className="w-5 h-5 text-green-600" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+                      <path strokeLinecap="round" strokeLinejoin="round" d="M9 12l2 2 4-4m6 2a9 9 0 11-18 0 9 9 0 0118 0z" />
+                    </svg>
+                    <span className="text-sm font-medium text-green-800">{t("moneyBackGuarantee")}</span>
+                  </div>
+
                   <button
                     type="submit"
                     disabled={isLoading || lines.length === 0 || !selectedShippingMethod}