[FEATURE] Add multi-language support (i18n)

[NovaCode37]

Add internationalization support to the frontend dashboard.

Scope:

• Add i18n framework (e.g. next-intl or next-i18next)
• Extract all UI strings into locale files
• Start with English (en) and Russian (ru)
• Language switcher in the Topbar

Implementation path:

File / Directory	Change
frontend/src/messages/en.json	English locale strings
frontend/src/messages/ru.json	Russian locale strings
frontend/src/components/Topbar.tsx	Language switcher dropdown
frontend/src/lib/i18n.ts	i18n config and provider setup
frontend/src/app/layout.tsx	Wrap app with i18n provider
frontend/package.json	Add next-intl dependency

Why:
PRISM has users from different countries. Multi-language support makes the tool more accessible and increases community adoption.