Add Russian localization

[DrMaks22]

Summary

• Add a lightweight English/Russian i18n layer with locale detection, persistence, and a language selector in the app chrome.
• Localize the core production UI into Russian, including project management, tracks, voices, inspector panels, timeline, transport, synthesis/export states, tooltips, and model progress messages.
• Add README.ru.md and link it from the existing English and Simplified Chinese README language switchers.

Notes

• Existing marker syntax such as <happy>, [excited], and engine/language names is intentionally preserved because it is part of synthesis behavior or product terminology.
• Packaging binaries used for local macOS installation are generated locally and remain ignored by git.

Validation

• pnpm test
• pnpm build
• swift build -c release
• cargo test --lib
• pnpm tauri build
• Installed and launched /Applications/Speech Studio.app locally; verified the app and sidecar start from the installed bundle.

[ivan-digital]

@DrMaks22 thanks for the Russian localization work.

I pushed one small maintainer fix on top: locale persistence now guards localStorage access so startup/tests do not crash when storage is unavailable or partially mocked.

Local tests/build passed, Linux CI is green, and Windows/macOS are still running. We will merge this once the current checks finish green.