fix: secure Node 20 runtime contract

[pitimon]

Summary

• upgrade direct production dependency undici from 7.27.1 to patched 7.29.0
• align the true CLI engine floor at Node 20.18.1+, matching Undici 7.x support
• remove the Node 22-only top-level node:sqlite dependency from the Hermes parser-conformance fixture
• add a dedicated exact-minimum Node 20.18.1 root-suite CI job while preparing dashboard-generated prerequisites under Node 24
• bump npm, macOS, and Windows versions in lockstep to 0.39.51

Verification

• RED contract: 0/3 passed before changes
• baseline Node 20.20.2 root suite: 1085/1086, failed on node:sqlite
• GREEN runtime contract: 3/3
• exact Node 20.18.1 root suite: 1098/1098
• proxy/redirect/body-limit/local API tests: 46/46
• Node 24 npm run ci:local: root 1098/1098; dashboard 42/42 files; OpenWiki 0
• npm audit --omit=dev --audit-level=high: 0 vulnerabilities
• publish dry-run: 0.39.51, 180 files, dashboard included
• version lockstep, outbound inventory, guardrails, secret scan, and git diff --check: passed

Fixes #167
Fixes #168