Security posture audit 2026-10-04: the 21 findings this repo owns (Closes #1018) - #1019

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: bufbuild/buf-setup-action@a47c93e0b1648d5651a065437926377d060baa99. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/