docs: polish README/CLAUDE.md wording and add fix-issue skill - #167

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: ts-graphviz/setup-graphviz@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/