Add CI workflow for build and quality checks

[Kodai Sakabe (koudaiii)]

This pull request introduces a new GitHub Actions workflow for continuous integration (CI) by adding a .github/workflows/ci.yml file. The workflow sets up automated build, test, and quality checks across multiple Node.js versions, and includes non-blocking quality gates for code formatting and dependency security.

CI workflow setup:

• Added .github/workflows/ci.yml to define a CI pipeline that runs on pull requests and pushes to main, covering Node.js versions 16, 20, and 24, with Node 24 marked as non-blocking due to known compatibility issues.
• Configured the build job to install dependencies, run TypeScript build, and perform a smoke test to ensure the action loads and fails gracefully if required inputs are missing.

Quality and security checks:

• Added a quality job that checks code formatting with Prettier and runs npm audit for high-severity vulnerabilities, both as non-blocking steps.