feat(triathlon): model and storage foundation - #648

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Deliberate short lag is fine — just make sure it's a conscious call, not a forgotten one. (This exact gap shipped edge a full day behind protocol's CRC8-length-check fix on 2026-07-30.)

openstrap_protocol is pinned at b4fde6ab5589e53154b808f8b2bbb4d01d9c15b5 but protocol's main has moved to fbadb5bd055965d9400e266d6cf42748992ba950.