- Add optional groupMembers parameter to both BuildHtml overloads and WriteAsync methods
- SharePoint group pills render as expandable with onclick toggleGroup when groupMembers provided
- Hidden member sub-rows injected after parent row with resolved member names
- Empty member list renders 'members unavailable' fallback label
- toggleGroup JS function added to inline script block in both overloads
- filterTable updated to skip data-group sub-rows
- CSS for .group-expandable added to both overloads
- Backward compatibility: null groupMembers produces identical output to pre-Phase 17
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