deps: bump to Nuxt 3.12, bring other dependencies up-to-date, separate prettier in repo & checks, update devcontainer.json format and docker container to Node.js to 20-bookworm

deps: bump to Nuxt 3.12, bring other dependencies up-to-date, separate prettier in repo & checks, update devcontainer.json format and docker container to Node.js to 20-bookworm #1189