e2e integration-tests (in CI-pipeline)

[elwinschmitz]

As a developer,
I want to know if every feature works and handles every type of input,
So that I can be confident that making changes/additions don't break existing instances of HIA.

---

It should have:

• a npm run test:e2e-script
• local test+set-up tools (just http-server? with a static production build?)
• tests written in a style/shape that is platform/framework 'independent'
  • web-component-testing-library? Web Test Runner?
  • Jest-or-similar? Most-used?
  • no TypeScript?
  • Vitest?
  • Also, see: https://dev.to/this-is-angular/angular-testing-in-2023-past-present-and-future-j5m
• test mock-data with all variations
  • multiple sheets
  • Different Environments
    • Offers-only
    • Q&A-only
    • mixed
    • Locale-Per-Sheet (See Add "regions are alternative languages"-mode (via ENV config) #762)
• Working test-pipeline in GitHub-Actions
  • using included, static mock-data
  • Reporter? Output?