feat: add English interface localization

[superdav42]

Summary

• add i18next-based English and Simplified Chinese interface localization
• add persistent interface-language selector and native Electron locale support
• localize project, settings, script, character, scene, director, S-Class, asset, media, export, Freedom, and shared UI surfaces
• add localized visual-style display metadata and catalog validation

Verification

• npm run validate:localization
• npx tsc --noEmit
• npm run build:desktop

Note: npm run lint still reports pre-existing repository-wide failures.