Summary

• enforce the grid table width from the computed column sizes so content cannot blow past the existing max width
• make writable cell content shrink correctly so oversized JSON and text values render with the standard ellipsis
• add regression coverage for both the table layout and writable cell display paths

Testing

• pnpm vitest ui/studio/cell/WriteableCell.test.tsx ui/studio/grid/DataGrid.layout.test.tsx ui/studio/grid/column-sizing.test.ts ui/studio/grid/DataGrid.virtualization.test.tsx
• pnpm typecheck

fixes #1357