refactor(datagrid): consolidate sort click cycle into header view

[datlechin]

Summary

Follow-up cleanup to #942. The three-state sort cycle (asc → desc → cleared) was split across two layers:

• Multi-column (shift-click): SortableHeaderView.mouseDown took over the click and called dataGridSort(..., isMultiSort: true) directly.
• Single-column (plain click): fell through to AppKit's two-state descriptor toggle, then tableView(_:sortDescriptorsDidChange:) post-hoc intercepted the desc → asc transition and rewrote it as "clear".

Two paths for the same UX, with the single-column path fighting AppKit's descriptor model. Any other code that produced a same-key desc → asc transition would have accidentally triggered clear.

This PR consolidates both paths into SortableHeaderView.mouseDown. The cycle decision is now a pure function (HeaderSortCycle.nextAction) and unit tested. tableView(_:sortDescriptorsDidChange:) and the isSyncingSortDescriptors reentry guard are deleted. tableView.sortDescriptors is still written one-way from the model in syncSortDescriptors for VoiceOver accessibility; nothing in our code reads it anymore.

Test plan

• Click an unsorted column header: sorts ascending, native indicator appears.
• Click again: descending.
• Click again: sort cleared, no indicator.
• Click again: ascending (cycle restart).
• Sort by column A, then plain-click column B: column B becomes primary ascending, column A clears.
• Shift-click a second column while column A is sorted: column A stays primary, column B added as secondary. Both indicators render.
• Shift-click the secondary column again: cycles its direction, primary unchanged.
• Drag a column boundary to resize: still works (boundary clicks fall through to super).
• VoiceOver on a sorted header: announces column name and sort direction.
• xcodebuild test — HeaderSortCycleTests (9 tests) and existing SortStateTests pass.
• swiftlint lint --strict — 0 violations.

[chatgpt-codex-connector]

💡 Codex Review

TablePro/TablePro/Views/Results/SortableHeaderView.swift

Lines 140 to 144 in 232a476

	switch action {
	case .sort(let columnIndex, let ascending, let isMultiSort):
	coordinator.delegate?.dataGridSort(
	column: columnIndex,
	ascending: ascending,

Fall through to AppKit for header drag interactions

SortableHeaderView.mouseDown now consumes every primary-button click on data-column headers by dispatching sort actions directly, but it never calls super.mouseDown in that path. That prevents AppKit from starting native header interactions (column drag-reorder, divider drag-resize, and divider double-click auto-fit), so users lose core table-header behavior as soon as the click lands on a sortable header.

---

TablePro/TablePro/Views/Results/DataGridViewDelegate.swift

Line 50 in 232a476

func dataGridClearSort() {}

Provide a non-noop default for clear-sort callback

The new single-column cycle emits .clear after descending, but the default dataGridClearSort() implementation is empty. Delegates that still only implement dataGridSort (for example the structure-grid delegate path) receive no state update on the third click, so the header remains stuck in descending and subsequent clicks on that same column keep resolving to clear with no effect.

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