Security policy, sponsor button, PR template, Dependabot for actions - #74

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/

Summary report available at: https://github.com/RadicalCSG/com.chisel/actions/runs/40344395380#summary-121647324628