feat: always install Node.js, upgrade to v22 and setup-node@v6 (#1)

* feat: always install Node.js, remove setup-node input

* chore: upgrade Node.js default to v22

* chore: update setup-node action to v6

* chore: update missing node error message

* docs: add inputs table, improve configuration examples, add secret guidance

feat: always install Node.js, upgrade to v22 and setup-node@v6 (#1)

* feat: always install Node.js, remove setup-node input

* chore: upgrade Node.js default to v22

* chore: update setup-node action to v6

* chore: update missing node error message

* docs: add inputs table, improve configuration examples, add secret guidance