Migrate to ESM with rollup and Node 24

[workflow]

Summary

Brings the repo infrastructure in line with the latest actions/typescript-action template:

• ESM: Added "type": "module", switched to import.meta.dirname, .js import extensions
• Rollup: Replaced @vercel/ncc with rollup for bundling dist/
• Node 24: Updated action.yml to node24, .node-version to 24.4.0
• Dependency updates: @actions/core ^3.0.0, eslint ^9, jest ^30, typescript ^5.9, prettier ^3.8
• New workflows: ci.yml (lint/test/format), check-dist.yml (ensures dist/ is up-to-date)
• Updated workflows: test.yml bumped to checkout@v6, setup-node@v6 with .node-version file
• Cleanup: Removed template leftovers (wait.ts, main.test.ts), deleted .prettierrc.json (use defaults), removed duplicate run() call
• README: Updated example YAML snippets to latest action versions