Add Simplified Chinese localization

[skyboooox]

Summary

• Added Simplified Chinese (zh-CN) localization support to the existing frontend i18n system.
• Registered zh-CN in language types, translation registry, and language selector labels.
• Updated language initialization so saved zh-CN preferences work and browser zh* locales default to Simplified Chinese.
• Migrated major visible UI strings to translation resources across login, sidebar, settings, dashboard, robot connection, health, missions, maps, audit/log, profile, and common console widgets.
• Added matching English, Portuguese, and Simplified Chinese translation keys for newly migrated UI text.

Validation

• npm run build:oss passed.
• Translation key consistency check passed for pt.ts and zh-CN.ts.
• git diff --check passed.
• Browser smoke tested language switching on the login page.
• Authenticated pages were reviewed through a local mock account only; no real Supabase credentials or secrets were added.

Notes

• npm run lint is currently blocked by the repository’s existing ESLint 9 flat config incompatibility with extends.
• Some deeper component text remains hardcoded, mainly in camera, chart, robot header, MapEditor tooltip, and specialized widget surfaces.