Add TreeGrid blog article

[cursor]

Summary

• Adds a new blog article highlighting the TreeGrid/tree-data feature from the docs.
• Covers TreeDataSource, TreeGrid, node paths, expand/collapse state, tree selection, custom tree icons, and Tree API actions.
• Adds a companion tweet draft beside the post.

Tweet draft

New on the Infinite Table blog: Tree DataGrids in React with TreeDataSource + TreeGrid.

Nested rows, node paths, expand/collapse state, selection, custom icons, and Tree API actions.

https://infinite-table.com/blog/2026/07/31/building-tree-data-react-datagrids-with-treegrid

Validation

• git diff --check HEAD~2..HEAD
• focused content script: Sandpack references exist, post/tweet ASCII-only, tweet is 276 chars
• npm --prefix www run tsc
• npm --prefix www run next-build