test: Add tests for DataTable suggestions panel

[annondeveloper]

The AI-powered suggestions panel (src/domain/data-table-suggestions.tsx) renders data analysis insights above the DataTable but has no test coverage.

What to test:

• Panel renders with suggestion list
• Confidence badges display correctly
• Click-to-apply triggers the suggestion action
• Dismiss removes individual suggestions
• Panel collapses/expands
• Empty state when no suggestions

Reference: See existing component tests in src/__tests__/components/ for patterns.
File to create: src/__tests__/domain/data-table-suggestions.test.tsx

Skills needed: React, TypeScript, @testing-library/react