docs: Japanese README to the latest version

[daikimatsura]

Issue # (if applicable)

Closes #144

Reason for this change

The Japanese documentation (README.ja.md) is significantly outdated compared to the current version of the project. This creates confusion for Japanese-speaking users who rely on this documentation to understand and use the project properly.

Description of changes

• Updated README.ja.md to match the content and structure of the current English README.md
• Translated new sections that were missing in the Japanese version
• Fixed outdated API descriptions and examples
• Updated installation instructions to reflect current methods
• Ensured consistent formatting between both language versions

Description of how you validated changes

• Manually reviewed each section against the English documentation to ensure accuracy
• Changed all code examples in the Japanese document to those in the current English document
• Had Claude-3.7-sonnet review it for clarity and accuracy

Checklist

• My code adheres to the CONTRIBUTING GUIDE
• I have updated the relevant documentation (if applicable).

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