Feature optimizations: i18n, layout button names, artifact fix, viewed checkbox

[Copilot]

Addresses four feature optimization requests: artifact workflow double-zip issue, layout button naming, i18n support, and viewed checkbox functionality.

Changes

Artifact Workflow

• Upload dist/chrome/ and dist/edge/ directories directly instead of zipping first
• Eliminates nested zip issue when downloading artifacts

Layout Button Naming

• Renamed "左右布局" → "Side-by-Side" and "上下布局" → "Unified"
• Standard diff terminology, localized via i18n

Internationalization

• Added _locales/{en,zh,ja}/messages.json with translations
• New i18n.js module: browser language detection, English fallback, localStorage persistence
• HTML uses data-i18n, data-i18n-title, data-i18n-placeholder attributes

Viewed Checkbox Feature

• Adds checkbox to each file header to mark files as "viewed"
• Checked files collapse (hide diff content) with green header styling
• State persisted to localStorage
• Enabled fileListToggle, fileContentToggle, stickyFileHeaders options

Screenshots

English UI:

Viewed checkbox (file1.txt collapsed):

Original prompt

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This section details on the original issue you should resolve

<issue_title>功能优化</issue_title>
<issue_description>1. artifact.yml目前打包结果 是 patchReader-chrome.zip下还有个同名的patchReader-chrome.zip 这样解压时会有问题，请去掉最外层的zip
2. 目前的左右布局和上下布局是针对差分视图的，目前名字不太合适，请帮我更换合适的名字
3. 支持国际化，中日英，默认是浏览器语言，如果都不符合，默认英文
4. diff2html 我记得课题有个viewed checkbox，可以折叠，能加上么，如果有其他的好用的功能也可以加上</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 功能优化 #8

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