feat: add TypeScript build infrastructure

[GoogilyBoogily]

Summary

Sets up TypeScript compilation for GitHub Action scripts. Complex bash logic in later PRs will be extracted into typed, testable .ts files compiled to dist/.

• package.json with @actions/core, @actions/exec, @actions/github deps
• tsconfig.json targeting CommonJS/ES2022, strict: true
• .nvmrc pinned to Node 24
• src/utils.ts: shared getRequiredEnv() helper used by all scripts
• dist/ committed to repo (required — consumers checkout and run node dist/script.js directly)
• .github/workflows/validate-scripts.yml: self-CI that builds and enforces dist/ stays in sync via git diff --exit-code dist/

Test plan

• npm ci && npm run build passes locally
• git diff --exit-code dist/ is clean after build
• validate-scripts workflow passes on this PR

[Copilot]

Pull request overview

This PR introduces TypeScript build infrastructure for the shared GitHub Actions repository so future action scripts can move from bash into typed source files compiled into committed dist/ output.

Changes:

• Adds npm/TypeScript project configuration and Node version pinning.
• Adds a shared getRequiredEnv() helper with compiled output in dist/.
• Adds CI validation to build TypeScript and verify dist/ is up to date.

Reviewed changes

Copilot reviewed 4 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.github/workflows/validate-scripts.yml	Adds self-CI to install dependencies, build scripts, and verify committed dist/.
.gitignore	Ignores local node_modules/.
.nvmrc	Pins the repo’s Node version to 24.
dist/utils.js	Adds compiled CommonJS output for the utility helper.
package-lock.json	Locks the newly added npm dependency tree.
package.json	Defines scripts and action-related TypeScript dependencies.
src/utils.ts	Adds a shared required-environment-variable helper.
tsconfig.json	Configures strict TypeScript compilation to dist/.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.