feat: 图形栈闭合与分发档位 —— 标签、一条没人依赖的边、一个被钉住的 pin (#405, #407) (2026.8.10.2) - #408

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