feat: add Chinese and English localization

[xinglongMedical]

Summary

• add shared English and Simplified Chinese locale handling with browser inference, English fallback, and persisted language selection
• add language switches to the Web UI and Admin UI while preserving user-authored, identity, secret, and server-provided content
• localize Web and Admin navigation, forms, notices, accessibility labels, statuses, dates, numbers, and controlled dynamic copy
• add regression coverage for locale resolution, dynamic UI sinks, and content-boundary collisions

Validation

• Web UI: 503 tests passed
• Admin UI: 81 tests passed
• root TypeScript check passed
• Web production build passed
• Prettier, ESLint, and git diff checks passed
• live browser QA passed at localhost:8129 for Web zh-CN -> en -> zh-CN and Admin zh-CN -> en -> zh-CN
• independent read-only i18n review: GO

Screenshots

Web — 简体中文

Web — English

Admin — 简体中文

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