- Rename HOW_TO_USE_EMAIL_REPLY.md to HOW_TO_USE_EMAIL_REPLY_ZH.md
- Rename HOW_TO_USE_EMAIL_REPLY_EN.md to HOW_TO_USE_EMAIL_REPLY.md
- Update all language switcher links accordingly
- English version is now the default (no language suffix)
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Co-Authored-By: Claude <noreply@anthropic.com>
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