Introduce Prettier and Enforce Indentation Rules via GitHub Actions

[henteko]

This pull request introduces code formatting improvements and automation:

• Added Prettier for consistent code formatting across the project
• Updated TypeScript files to conform to defined indentation rules
• Configured GitHub Actions to automatically check formatting on each push and pull request

These changes help maintain code style consistency and prevent formatting issues in future contributions.

[Copilot]

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

Files not reviewed (2)

• .prettierrc: Language not supported
• package.json: Language not supported

[enomoto-kazuya]

LGTM! Thank you for formatting.

[henteko]

Thanks!