i18n: add landing page translations (en/ru)

Added/updated translations for:
- howto: step labels
- stats: suppliers desc, countries
- testimonial: quote, author, role
- roles: subtitle, updated benefits
- cta: register, demo buttons
- footer: all countries, offices, products, services, legal

i18n/locales/en/testimonials.json

@@ -1,5 +1,10 @@
 {
   "testimonials": {
     "title": "Client Testimonials"
+  },
+  "testimonial": {
+    "quote": "Optovia helped us find reliable suppliers in just days. It used to take months.",
+    "author": "Alexey Petrov",
+    "role": "Procurement Director, AgroHolding"
   }
 }