feat(i18n): add Simplified Chinese (zh-CN) localization

[renfei]

Summary

• Add src/i18n/locales/zh-CN.json with full Simplified Chinese translations covering all existing keys (common, header, hero, features, instructions, status, errors)
• Register zh-CN as a supported language in src/i18n/config.ts
• Add 简体中文 option to the language selector dropdown in LanguageSelector.tsx

Changes

File	Change
src/i18n/locales/zh-CN.json	New file — complete zh-CN translation
src/i18n/config.ts	Import and register zh-CN resource
src/components/LanguageSelector.tsx	Add { value: 'zh-CN', label: '简体中文' } to language list

Testing

1. Open the app in a Chromium-based browser
2. Open the language selector
3. Choose 简体中文
4. Verify all UI strings are displayed in Simplified Chinese

Summary by CodeRabbit

• New Features
  • Added Simplified Chinese language support. Users can now select Simplified Chinese as their preferred language for the app interface, with complete translation coverage for all UI elements, including navigation, features, and system messages.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 09900b8a-11b5-4991-a4e9-323ab604ec8c

📥 Commits

Reviewing files that changed from the base of the PR and between 3b94164 and 4f10947.

📒 Files selected for processing (3)

• src/components/LanguageSelector.tsx
• src/i18n/config.ts
• src/i18n/locales/zh-CN.json

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📝 Walkthrough

Walkthrough

Adds Simplified Chinese (zh-CN) language support by introducing a new locale JSON file with 78 translation keys, registering it in the i18next configuration, and adding it as a selectable option in the LanguageSelector component.

Changes

Simplified Chinese Localization

Layer / File(s)	Summary
zh-CN locale file and i18next registration src/i18n/locales/zh-CN.json, src/i18n/config.ts	Adds zh-CN.json with translations for all UI areas (labels, navigation, hero, features, instructions, flash/log status strings, and browser error), imports it in config.ts, and registers it under 'zh-CN' in the i18next resources map.
LanguageSelector UI entry src/components/LanguageSelector.tsx	Adds zh-CN (Simplified Chinese) to the languages array so it appears as a selectable option alongside the existing entries.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A bunny hops east, past the Great Wall so grand,
New words bloom like flowers across the land.
zh-CN now lives where only one tongue had been,
Each key unlocks a phrase for eyes yet unseen.
Hào! The flasher speaks Chinese — how grand a sight! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding Simplified Chinese (zh-CN) localization support across multiple files (translation file, i18n config, and language selector).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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