Add KAKEHASHI case study to README

[dyoshikawa]

Summary

• add the KAKEHASHI Tech Blog article to the Case Studies section in the README
• whitelist the new case study name in cspell

Testing

• pnpm cicheck

---

Codex Task

[Copilot]

Pull request overview

This PR adds a new case study from KAKEHASHI Tech Blog to the README's Case Studies section. The change demonstrates growing adoption of Rulesync by Japanese tech companies.

• Adds KAKEHASHI Tech Blog article to the Case Studies section
• Updates cspell.json to whitelist "KAKEHASHI"

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cspell.json	Adds "KAKEHASHI" to the spell-check whitelist to prevent false positives
README.md	Adds KAKEHASHI Tech Blog case study entry with Japanese title and link

---

The changes look good! The formatting is consistent with existing case study entries, and the cspell whitelist has been properly updated. The Japanese title in the link text is appropriate for a Japanese tech blog article, and the URL structure follows the same pattern as the Asoview entry. No issues found.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.