Use TypeScript for plugin package checks

[nicu-chiciuc]

Summary

• add the package metadata and keep version 0.2.0 equal across package and plugin manifests
• replace the MJS check with a native TypeScript check
• run the package check in CI on pull requests and main
• document pnpm check as the one validation command

Why

This gives the plugin repository one package command and detects version drift before release.

Validation

• pnpm check
• node --check scripts/check.ts
• node scripts/check.ts
• claude plugin validate . --strict
• claude plugin validate ./plugins/samebase --strict
• no .mjs files or references remain