CI: install, build (incl. tsc) and lint on every PR - #8

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

public/coi-serviceworker.js:145:17: Expected expression to be used

public/coi-serviceworker.js:139:21: Expected expression to be used

public/coi-serviceworker.js:132:21: Expected expression to be used

public/coi-serviceworker.js:129:17: Expected expression to be used

public/coi-serviceworker.js:123:13: Expected expression to be used

public/coi-serviceworker.js:117:13: Expected expression to be used

public/coi-serviceworker.js:102:17: Expected expression to be used