Add blog post about pivoted React DataGrids

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Summary

• Adds a new Infinite Table blog article highlighting the pivoting docs feature.
• Covers generated pivot columns, custom pivot headers, total/grand-total columns, and links back to the relevant docs.
• Embeds the existing docs demos for pivoting and pivot total columns.

Suggested tweet

Build cross-tab reports in React without handcrafting every column.

Our new Infinite Table article shows how DataSource pivoting generates DataGrid columns from your data, while still letting you customize headers, totals, and formatting.

Read it here: https://infinite-table.com/blog/2026/07/10/building-pivoted-react-datagrids-with-generated-columns

Validation

• npm run index-content in www completed successfully and generated the new route.
• npm --prefix source run build completed successfully.
• npm --prefix www run next-build compiled successfully, then failed during TypeScript validation on an existing www/dataserver/cli.ts commander typing issue: Property 'InvalidArgumentError' does not exist on type 'CommanderStatic'.