fix: make npm run test runnable and enforce it in CI

[dubadub]

Fixes #84. See this comment for the full trace — my original diagnosis in the issue body was wrong, and the corrected one is what this PR acts on.

Two independent blockers, neither a bug in the tests themselves.

1. Wrong Node version

CLAUDE.md documented Node.js ≥18.17.0, <21. The root package.json requires >=22, and CI uses 22 — so the contributor-facing docs pointed at exactly the versions where the suite cannot load.

On Node 20 a CommonJS spec that requires an ESM module (any browser spec reaching @theia/monaco-editor-core) takes the synchronous require(esm) loader, which ignores the hooks @theia/test-setup registers via register():

$ node --version && node node_modules/.bin/_mocha ... prompt-variable-contribution.spec.js
v20.19.1
 Exception during run: TypeError [ERR_UNKNOWN_FILE_EXTENSION] ... aria.css

$ /usr/local/bin/node --version && /usr/local/bin/node node_modules/.bin/_mocha ... prompt-variable-contribution.spec.js
v23.10.0
  11 passing (87ms)

Worse, mocha retries a failed import with require, so the spec is partially executed twice and the retry surfaces The configuration is already set. — burying the real error entirely.

Fix: correct the documented requirement, add .nvmrc (22), and fail fast in @theia/test-setup with the actual reason:

✖ ERROR: Error: Theia tests require Node.js >= 22, but this is Node 20.19.1. Run `nvm use` (see .nvmrc) and try again.

2. Spec-less packages abort the run

@theia/cooklang-account and @theia/cooklang-branding declared "test": "theiaext test" but contain no spec files. Mocha exits non-zero on No test files found, and test:theia runs --concurrency=1 under nx bail — so the run stopped there and skipped ~40 packages. Upstream only declares the script where specs exist; these two now match, and the "adding a new package" checklist in CLAUDE.md calls it out.

Result

$ npm run test:theia
 Lerna (powered by Nx)   Successfully ran target test for 40 projects

1936 tests passing, 0 failing.

Added as a Test step in pr.yml, which until now ran only compile and lint — which is why this went unnoticed. test:electron is deliberately excluded: it needs a display server and the packaged app, so wiring it up means xvfb and a different kind of flake budget.

Note for reviewers

This PR does not change any test or product code — only docs, .nvmrc, two package.json scripts, a Node version guard, and the CI step. The Test step is new and unproven on CI hardware; if it turns out slow or flaky there, the cheap fallback is to keep it but mark it non-blocking.