Fix: update API test script to target files and add regression check (Fixes #4111)

[mvmax-dev]

This PR fixes issue #4111.

Problem

The API package test script in apps/api/package.json was configured to run node --test src/tests. Because it targeted the directory instead of files, the Node.js test runner failed with MODULE_NOT_FOUND error when trying to resolve apps/api/src/tests.

Solution

1. Updated the test script inside apps/api/package.json to target concrete test files: node --test src/tests/*.test.js.
2. Implemented a new regression check file apps/api/src/tests/package.test.js that reads package.json and asserts that the test script targets the files correctly and doesn't fall back to targeting the directory.

All tests passed successfully:

> test
> node --test src/tests/*.test.js

TAP version 13
# Subtest: GET /health returns ok payload
ok 1 - GET /health returns ok payload
  ---
  duration_ms: 41.828506
  type: 'test'
  ...
# Subtest: package.json test script regression check
ok 2 - package.json test script regression check
  ---
  duration_ms: 0.669546
  type: 'test'
  ...
1..2
# tests 2
# suites 0
# pass 2
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 244.246914

Closes #4111