Modernize toolchain: deps refresh, esbuild + Vitest

[skaji]

Summary

• Upgrade dependencies, including @actions/*, and align Node typings to Node 24
• Migrate build pipeline from ncc to esbuild
• Modernize TS/module settings and keep action runtime output stable
• Replace Jest with Vitest and rename test directory from __tests__ to tests
• Update CI workflow actions to latest major versions (actions/checkout@v6, actions/setup-node@v6)

Note

• For GitHub Actions runtime compatibility, the distributed bundle (dist/index.js) is built as CommonJS.

close #46