feat(i18n): full EN/UK/RU coverage — app pages, landing, AppLayout switcher
- Add LanguageSwitcher to AppLayout header (all authenticated pages)
- Fix Pricing tooltip: remove nested TooltipProvider (broken hover popup)
- Landing: FAQ, HowItWorks, Comparison, Testimonials, FeatureGrid, Footer
- App pages: Dashboard, Admin, MyUsage, Billing
- Toast messages: FocusGroups, SyntheticUsers, FocusGroupSession (28 toasts)
- New namespaces: faq, how_it_works, comparison, testimonials, features,
footer, dashboard, admin, usage, billing, focus_groups, synthetic_users,
focus_group_session — 130+ keys across EN/UK/RU
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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