ru-RU was missing most AI-chat keys, so the chat/typing widgets rendered
mixed-language (some keys fell back to en-US). Fill the full AI-chat string
set in ru-RU and document the maintenance policy.
- ru-RU/translation.json: add the 24 missing AI-chat keys (labels, typing
indicator, Ask-AI widget, public-share, error messages); keep the typing
keys grouped; existing translations untouched.
- i18n.ts: add a policy comment near fallbackLng — en-US is the source of
truth; en-US + ru-RU are fully maintained; the other 10 locales
intentionally rely on the en-US fallback until contributed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>