feat: add i18n support for Chinese and English CLI

[ironfrancis]

Summary

Add internationalization (i18n) support for HarnessCode CLI, allowing users to switch between English and Chinese interface while keeping source code comments and logs in English.

Features

• hc config language zh - Switch to Chinese interface
• hc config language en - Switch to English interface
• HARNESSCODE_LANGUAGE=zh hc - Use environment variable for language

Changes

New Files

• src/harnesscode/utils/i18n.py - i18n module with translation loader
• src/harnesscode/locales/en.json - English translations
• src/harnesscode/locales/zh.json - Chinese translations

Modified Files

• src/harnesscode/cli.py - Added translation support and hc config command
• src/harnesscode/installer.py - Updated user-facing messages to use translations
• src/harnesscode/infinite_dev.py - Updated interactive prompts (model selection, branch selection)
• src/harnesscode/restore_config.py - Updated restore messages
• src/harnesscode/utils/config.py - Added get_language_from_config() function
• README.md - Added language configuration documentation
• README_CN.md - Added language configuration documentation

Design Principles

• Source code comments and logs remain in English
• Only user-facing prompts support translation
• Default language is English (backward compatible)
• Centralized translation management in JSON files
• Easy to add more languages in the future

Testing

Tested the following scenarios:

• English help display (hc, hc --help)
• Chinese help display (HARNESSCODE_LANGUAGE=zh hc)
• Configuration view (hc config)
• Language switching via config and environment variable

Usage

# View current configuration
hc config

# Switch to Chinese
hc config language zh

# Switch to English
hc config language en

# Or use environment variable
HARNESSCODE_LANGUAGE=zh hc