fix: exit non-zero when tests fail

[itskodama]

The problem

test counts failed tests and prints the total, then returns normally:

console.log('    Passed:', pc.green(passedTests))
console.log('    Failed:', pc.red(failedTests))
}

There is no process.exit or process.exitCode anywhere in the command, so the
process always ends with status 0. Failed: 4 and Failed: 0 look identical to
anything downstream, which makes the command unusable as a CI gate.

The change

if (failedTests > 0) {
  process.exitCode = 1
}