feat(ui): add Russian (ru) localization

[artur-shaikhutdinov]

Closes #649

Summary

• ui/messages/ru.json: a complete Russian catalog for all 1,288 message keys. Placeholders, product names and commands are kept as they are. The catalog has no plural forms, so count strings are worded to read correctly with any number (Экспериментов: {count}).
• ui/project.inlang/settings.json: ru added to the locales.
• ui/index.html: ru added to the browser-language check that runs before the first paint.
• SettingsPage.tsx: Русский added to the language picker.
• README.ru.md: a translation of the README, and every README's language row links to it.
• ui/dist regenerated.

The files changed follow the Polish localization (#626).

Test plan

• check-i18n and check-styles
• pnpm typecheck and 261 UI tests
• vite build matches the committed ui/dist
• CI on the branch in my fork (fmt, clippy, test; Windows; Linux app)
• The same translation ships in my fork's 0.3.8 release, checked on Windows: Settings → Language → Русский

[greptile-apps]

Confidence Score: 5/5

[Low impact] This PR appears safe to merge.

Summary

Adds Russian translations and makes Russian available through browser language detection and the settings picker.

• Russian users can choose Russian for the OpenResearch interface.
• Russian readers can use a translated project guide.

_{Reviews (1) · Last reviewed commit: "Add a Russian localization of the dashbo..." · Reviewed by Greptile}