feat: typed cells, custom columns, and self-owned column persistence - #5

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, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

src/lib/grid/phoneCell.tsx:77:14: Fast refresh only works when a file only exports components. Use a new file to share constants or functions between components.

src/lib/grid/phoneCell.tsx:65:17: Fast refresh only works when a file only exports components. Use a new file to share constants or functions between components.