Adds a short plain-language description under each field label (new
.field-desc style, section.shared.scss) so a non-developer admin
understands what each field affects, per i18n (en/ru/hy) convention.
Only General and Branding sections are wired up so far - the *Desc i18n
keys for the remaining sections (theme/header/footer/homepage/widgets/
features/languages/navigation) were prepared in translations.ts/en/ru/hy
but not yet wired into their templates. Follow-up work.
