Use of Docker Compose in `app`

[akauppi]

This will fix #67 and allow CI to run Cypress tests.

Current problems:

• running Vite within Docker Compose means HMR doesn't work

Follow https://github.com/vitejs/vite/issues/4116 for the HMR issue.

[akauppi]

• [ ] Test next-docker-compose branch on Windows + WSL2

Let's close this once the developer experience works, and the code is merged to (at least) next.

[akauppi]

Merged also somewhat accidentally to master #73

Remains:

• [. ] running Cypress tests
• [. ] solving why HMR doesn't work from within Docker Compose