Add Simplified Chinese (zh-CN) admin locale

[ayfl269]

What does this PR do?

Adds Chinese (Simplified) translation for the EmDash admin UI. This enables Chinese-speaking users to use the admin interface in their native language.

Changes included:

• Add "zh-CN" to lingui.config.ts locales array
• Register { code: "zh-CN", label: "简体中文" } in the admin SUPPORTED_LOCALES
• Add initial messages.po with 36 translated messages at packages/admin/src/locales/zh-CN/messages.po
• Translate all admin UI strings including login page, settings page, and locale switching interface
• Preserve all placeholders ({email}, {label}, {error}) and Lingui component markers (<0>...</0>)

Translation coverage:

• Login page (magic link authentication, passkey, email sign-in)
• Settings page (general, security, SEO, API tokens, language preferences)
• Locale switching interface (language selector, translation status indicators)

Type of change

• Bug fix
• Feature (requires https://github.com/emdash-cms/emdash/discussions/categories/ideas )
• Refactor (no behavior change)
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read https://github.com/emdash-cms/emdash/blob/main/CONTRIBUTING.md
• pnpm typecheck passes ✅ (CI passed)
• pnpm --silent lint:json | jq '.diagnostics | length' returns 0 ✅ (CI passed)
• pnpm test passes (or targeted tests for my change) ✅ (CI passed)
• pnpm format has been run ✅ (CI passed)
• I have added/updated tests for my changes (if applicable)
• I have added a https://github.com/emdash-cms/emdash/blob/main/CONTRIBUTING.md#changesets (if this PR changes a published package)
• New features link to an approved Discussion: https://github.com/emdash-cms/emdash/discussions/...

AI-generated code disclosure

• This PR includes AI-generated code

Test output

CI Results:

• ✅ Format: Passed
• ✅ CI (Type Check, Lint, Test, Build): Passed
• ✅ PR Compliance: Passed

Translation example:

msgid "Sign in to your site"
msgstr "登录到您的网站"

msgid "Send magic link"  
msgstr "发送免密登录链接"

msgid "Settings"
msgstr "设置"

All core CI checks (Format, CI, PR Compliance) have passed successfully. The translation files will be compiled during the build process in the main repository.

Resolving conflict issues #455

[changeset-bot]

🦋 Changeset detected

Latest commit: e2af806

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 15 packages

Name	Type
@emdash-cms/admin	Patch
emdash	Patch
@emdash-cms/cloudflare	Patch
@emdash-cms/plugin-ai-moderation	Patch
@emdash-cms/plugin-atproto	Patch
@emdash-cms/plugin-audit-log	Patch
@emdash-cms/plugin-color	Patch
@emdash-cms/plugin-embeds	Patch
@emdash-cms/plugin-forms	Patch
@emdash-cms/plugin-webhook-notifier	Patch
@emdash-cms/auth	Patch
@emdash-cms/blocks	Patch
@emdash-cms/gutenberg-to-portable-text	Patch
@emdash-cms/x402	Patch
create-emdash	Patch

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commit: e2af806