Add BRABUS-focused homepage SEO copy

[alanw707]

Summary

• Rework homepage hero copy around genuine BRABUS parts and Mercedes-Benz/G-Class upgrade keywords
• Add BRABUS-focused language to SEO accordion, FAQ/schema answers, trust strip, vendor strip, category cards, and blog teaser
• Keep changes content-only; no URL/category restructure

Checks run locally

• npm run lint:css passed
• npm run lint:js passed
• npm run build passed
• PHP syntax check will run in GitHub Actions