feat(dashboard): add Simplified Chinese (zh) translations

[whtis]

Description

Adds a Simplified Chinese (zh) locale to the dashboard, following the i18n pattern introduced by #64. Chinese is now selectable from the sidebar language switcher alongside English and Hebrew.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

What's included

• dashboard/src/i18n/locales/zh.json — new locale file mirroring the structure of en.json. All 404 leaf keys translated; one new common.chinese label added for the language menu.
• dashboard/src/i18n/index.ts — zh registered in supportedLanguages and resources so i18next-browser-languagedetector picks up zh-* browsers automatically.
• dashboard/src/components/Layout.tsx — replaced the he / EN ternary in languageLabel with a Record<SupportedLanguage, string> lookup. zh displays as 中文. The lookup makes the next locale a single-line addition.
• dashboard/src/i18n/locales/en.json — added common.chinese: "中文" for parity with the existing common.english / common.hebrew entries.

Why

The Hebrew i18n PR (#64) just added the language switcher and a second locale. This drops in a Simplified Chinese translation so the Chinese-speaking community can use the dashboard without falling back to English, and to validate that the existing i18n module scales to a third language without infrastructure changes (no RTL, no font, no CSS).

How tested

• npm run build in dashboard/ — tsc -b clean, vite build succeeds.
• npm run lint — 0 errors, 3 pre-existing warnings unrelated to this change.
• Key parity check: en.json and zh.json have identical key trees apart from the intentional common.chinese addition. Script:

  import json
  en = json.load(open('dashboard/src/i18n/locales/en.json'))
  zh = json.load(open('dashboard/src/i18n/locales/zh.json'))
  # … flatten & diff -> only extra key is common.chinese

• Chinese strings present in the production bundle (grep "审计日志\|仪表盘" dist/assets/index-*.js).

Notes

• Backwards compatible. English remains the fallback (fallbackLng: 'en'). Existing users see no change unless their browser is zh-* or they pick 中文 from the switcher.
• Translation choices:
  • Brand / product names kept in English: OpenWA, WhatsApp, BullMQ, MinIO, PostgreSQL, SQLite, Redis, S3, TypeORM, Webhook (very widely used as-is in zh-CN tech writing — translating to "网络钩子" reads worse than keeping it).
  • Common terms translated: Session → 会话, Dashboard → 仪表盘, API Key → API 密钥, QR Code → 二维码, Audit Logs → 审计日志.
  • Placeholders ({{count}}, {{name}}, {{message}}) and inline HTML (<strong>, <code>, <br/>) preserved exactly.
• No RTL support needed (Chinese is LTR), so rtlLanguages is unchanged.

Screenshots

N/A — visible change is the sidebar language button cycling to 中文 and dashboard labels rendering in Chinese; reviewers can verify locally via npm run dev and clicking the language toggle.

Related Issues

None.

Drafted with AI assistance; verified by author before publishing.