feat: publish shared configure-nodejs action

[huntharo]

Summary

I extracted the configure-nodejs logic into this standalone repo so it can be shared as pwrdrvr/configure-nodejs@v1.

I added:

• a root-level composite action with working-directory-aware manager and cache resolution
• helper scripts and direct Node tests for package-manager and cache-path behavior
• isolated npm, pnpm, and Yarn fixtures with matrix CI coverage using the local action
• README and tag-driven release workflow documentation for publishing and maintaining the v1 tag

Testing

I verified this works end to end locally:

• source ~/.nvm/nvm.sh && nvm use 22 >/dev/null && npm test
• source ~/.nvm/nvm.sh && nvm use 22 >/dev/null && npm ci && node check.mjs in fixtures/npm-basic
• source ~/.nvm/nvm.sh && nvm use 22 >/dev/null && corepack enable && pnpm install --frozen-lockfile && node check.mjs in fixtures/pnpm-basic
• source ~/.nvm/nvm.sh && nvm use 22 >/dev/null && corepack enable && yarn install --immutable && node check.mjs in fixtures/yarn-basic
• YAML parse checks for action.yml, .github/workflows/ci.yml, and .github/workflows/release.yml
• git diff --check

Post-Deploy Monitoring & Validation

No additional operational monitoring required because this change creates a standalone GitHub Action repository and CI workflows only; it does not change a running production service.