Run the unit tests in CI, and fail the gate when none run

[systemslibrarian]

From the findings in systemslibrarian/crypto-lab#2 ("the unit-test step runs 0 tests").

Why no tests ran

The unit tests are TypeScript that Node runs through its own type stripping (import … from './oracle.ts'). The deploy workflow pinned Node 20, which has no type stripping, so node --test never looked at .ts files. It found nothing to run and exited 0. The latest main build (run 35186536668, commit e57bb57) logged:

# tests 0
# pass 0
# fail 0

and the gate passed.

The fix

• CI uses Node 24. The same test files load, and 13 tests run.

• npm test now runs scripts/test.mjs. This drives node:test's own runner over src/**/*.test.ts and exits non-zero if:

  • no file matches;
  • the matched files define no tests (node:test reports such a file as one passing "test" named after the file, so those are subtracted);
  • any test fails.

  node --test alone exits 0 on an empty run, even for a glob that matches nothing.

Checked locally before pushing: the real suite passes with 13 tests. Each failure case exits 1: a pattern matching no files, a matched file with no tests, and a failing test. Loading the runner under Node 20 fails immediately rather than passing.

Test count from this PR's CI log

From this PR's run (35753742748, commit bfa6c00), step Run tests:

node-version: 24
Run npm test
ℹ tests 13
ℹ pass 13
ℹ fail 0
Unit tests run: 13

On main, the same step (run 35186536668) reported # tests 0.

Nothing else changed: no test, source or other workflow step.

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