feat(SEO): enhance product and category JSON-LD with shipping and return policy details

- Added merchant return policy and shipping details to the JSON-LD for both product and category schemas.
- Updated delivery method price to reflect the new shipping rate of 5.90 €.
- Improved localization files to include loading messages for products and updated various translations for consistency.

src/i18n/locales/en/delivery.js

@@ -16,7 +16,7 @@ export default {
   "prices": {
     "free": "free", // kostenlos
     "freeFrom100": "(free from 100€)", // (kostenlos ab 100€)
-    "dhl": "6.99 €", // 6,99 €
+    "dhl": "5.90 €", // 5,90 €
     "dpd": "4.90 €", // 4,90 €
     "sperrgut": "28.99 €" // 28,99 €
   },