Add bilingual Chinese TermKit Studio interface

[ZilaiWang]

What changed

• adds a centralized Chinese/English locale provider with browser-local preference persistence
• defaults new Studio sessions to Simplified Chinese while retaining an English toggle
• localizes navigation, commands, semantic status/policy/rights indicators, and all primary Studio workspaces
• preserves TermSpec enum values, language tags, stable IDs, and canonical terminology content
• refreshes embedded production assets and documents localization behavior
• adds localization unit coverage and Playwright coverage for default Chinese, language switching, and persistence

User impact

Chinese-speaking curators can now use the full Studio workflow in Simplified Chinese without creating a separate UI or changing canonical pack data. Existing users can switch back to English from the top bar.

Validation

• TypeScript check passed
• 4 Vitest files / 8 tests passed
• 3 Playwright E2E tests passed
• production frontend build and embedded asset consistency checks passed
• real-browser visual and interaction QA completed