DataTable primitive (decide: standalone or TreeTable-with-depth-0)

[JDonaghy]

Part of the cross-platform UI crate (see docs/UI_CRATE_DESIGN.md).

What

A flat grid primitive: rows × columns, sortable columns, resizable columns, cell selection, cell editing. No hierarchy.

Use cases:

• SQL client: query result grids (thousands of rows, paging)
• k8s dashboard: resource list views
• vimcode: quickfix list as a table (file, line, severity, message), find/replace preview

Decision needed

DataTable may be redundant with TreeTable (see sibling issue): a TreeTable with max_depth = 0 is a flat data table. Options:

1. Ship TreeTable only — apps pass rows with no children. Simpler API surface.
2. Ship TreeTable + DataTable as distinct primitives — DataTable is more optimized for large flat data (virtual scrolling, column freezing, bulk selection), with no indent/expand overhead.
3. Ship all three — TreeView, DataTable, TreeTable — each tuned for its scenario.

Recommendation: start with option 1 (TreeTable only) and fork to a dedicated DataTable if profiling shows the tree-generalization costs too much for large flat datasets.

Acceptance

A decision documented in the design doc, plus implementation if option 2 or 3 is chosen.