[Blankll]

Closes the dockit portion of wentsen/geekfun#79

What

Adds pt-BR, Japanese, Korean, and Spanish to DocKit, with full translations of all UI strings.

• src/lang/: four new catalogs (ptBR, jaJP, koKR, esES, 1789 keys each), registered in the i18n setup with system-language detection extended (pt* / ja* / ko* / es* prefixes; zh-TW/HK/MO/Hant unchanged). Missing keys now fall back to enUS because the config gained an explicit fallbackLocale.
• Settings picker: the four languages appear under Settings → Basic → Language. This also fixes an old bug in the picker — any non-Chinese selection was previously mapped back to English, so choosing a new locale used to display English regardless. AUTO now delegates to the same detection the startup path uses.
• getDocLanguage() still returns 'en' for the four new locales, since docs and agent prompts ship only in English and Chinese.
• tests/i18nParity.test.ts: every locale file must carry exactly the enUS key set; CI now fails on drift instead of silently rendering English at runtime.
• docs/I18N.md: documents the setup and the steps to contribute another language.
• README: four new translations plus the expanded language navigation line.

Verification

• npx jest tests/i18nParity.test.ts — 6 locales, all key sets identical to enUS (1789 keys)
• vue-tsc --noEmit clean
• Existing tests unaffected

[codecov]

Codecov Report

❌ Patch coverage is 78.26087% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.26%. Comparing base (492b4f7) to head (768c541).

Files with missing lines	Patch %	Lines
src/lang/index.ts	70.58%	0 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #546      +/-   ##
==========================================
+ Coverage   72.21%   72.26%   +0.04%     
==========================================
  Files         171      174       +3     
  Lines       29769    29701      -68     
  Branches     1509     1514       +5     
==========================================
- Hits        21498    21463      -35     
+ Misses       7810     7772      -38     
- Partials      461      466       +5     

Files with missing lines	Coverage Δ
src/lang/enUS.ts	100.00% <ø> (ø)
src/lang/esES.ts	100.00% <100.00%> (ø)
src/lang/jaJP.ts	100.00% <ø> (ø)
src/lang/koKR.ts	100.00% <ø> (ø)
src/lang/ptBR.ts	100.00% <100.00%> (ø)
src/lang/zhCN.ts	100.00% <ø> (ø)
src/lang/zhTW.ts	100.00% <ø> (ø)
src/store/appStore.ts	51.55% <100.00%> (+0.76%)	⬆️
src/lang/index.ts	86.84% <70.58%> (-13.16%)	⬇️

... and 4 files with indirect coverage changes

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