Add native production smoke checks

[sonukapoor]

This turns part of the 0.x production-readiness roadmap from #8 into a small native smoke path. It is not a production-readiness gate or release sign-off; it gives future readiness work a repeatable starting point for basic runtime checks.

The PR adds make test-production-readiness, a shell runner, two native fixtures, and a short roadmap doc. The first smoke set covers the version path, eval path, built-in module loading, HTTP loopback lifecycle, and repeated cold starts. Each case has a timeout so a stuck runtime invocation fails the smoke run instead of hanging indefinitely.

Safe-mode smoke remains optional with EDGE_PRODUCTION_READINESS_SAFE=1, and network/TLS safe-mode coverage stays on the existing make test-wasix-safe-mode path.

I verified this locally with:

bash -n scripts/run-production-readiness-smoke.sh
git diff --check
make test-production-readiness

The local native smoke run passed 5 checks with 0 failures.

[sonukapoor]

@syrusakbary CI is green now after the unrelated WASIX smoke instability was fixed across the open branches.

This PR is scoped to a small native production-readiness smoke set for the 0.x roadmap. If the scope looks aligned, I think it is ready for review.