Add Phase 1 smoke test

[enricopiovesan]

Summary

• Makes scripts/ci/phase1_smoke.sh executable (was -rw-r--r--)
• Changes no-runtime behavior from FAIL (exit 1) to SKIP (exit 0) — CI without a configured runtime now passes cleanly with a skip notice
• Removes continue-on-error: true from nightly workflow — the step is now a real gate; set the TRAVERSE_RUNTIME_URL repo variable to activate it against a live runtime

Closes #5

Definition of Done

• Smoke test starts or connects to local Traverse runtime
• Verifies: execute → poll → output fields present
• Output is concise and CI-friendly
• Exits 0 on pass or when no runtime is configured (skip); exits 1 with detail on failure

Validation

# No runtime — clean skip
bash scripts/ci/phase1_smoke.sh  # → SKIP, exit 0

# With runtime
TRAVERSE_RUNTIME_URL=http://127.0.0.1:8787 bash scripts/ci/phase1_smoke.sh