Upgrade Babel to 8 together with Jest's Babel deps (#7252) #7277

Problem

Dependabot's #7252 bumps @babel/core from 7.29.7 to 8.0.7. It fails npm_lint, rspec and docker at npm install with ERESOLVE, before any test runs:

babel-jest@"30.5.1" from jest-config@30.5.1
dev @babel/preset-env@"^7.29.7" from the root project

babel-jest (Jest 30) and @babel/preset-env@^7 both need @babel/core 7, so @babel/core can't move to 8 by itself.

Context

• Babel is only used for Jest (babel.config.js; npm run test). The app's JS is bundled by ESBuild (bin/asset_bundling_scripts/build_js.js), which doesn't use Babel. So this only affects the test toolchain, never production code.

Tasks

• Find out whether babel-jest / Jest and @babel/preset-env have releases that support Babel 8 yet
• If yes: one PR bumping @babel/core, @babel/preset-env and babel-jest/Jest together. Check babel.config.js against the Babel 8 migration guide, and make sure npm run test passes.
• If no: add an ignore for @babel/* major versions to the npm entry in .github/dependabot.yml (with a comment linking this issue), and close build(deps): bump @babel/core from 7.29.7 to 8.0.9 #7252
• Optional: try whether Jest can drop Babel entirely, e.g. via a native ESM or ESBuild-based transform

Difficulty: intermediate. Good for someone who likes JS tooling.