Add option to mark first column as row headers

Problem/Motivation

For proper table accessibility, the first column should be able to be marked as row headers (<td> elements) instead of data cells (<td>). This is especially important when the first column contains category names, labels, or identifiers that describe each row.

WCAG 2.1 requires proper table markup with header cells to help screen reader users understand table relationships.

Proposed resolution

Add a checkbox configuration option: "First column of table is a row header"

When enabled, use DataTables columnDefs cellType option to render first column cells as <td> instead of <td>.

Remaining tasks

• [ ] Add checkbox to field widget settings
• [ ] Implement DataTables columnDefs configuration
• [ ] Test with screen readers
• [ ] Verify table semantics with accessibility validators