fix(search): restore the column show/hide menu and shift+page selection

[got3nks]

Two more behaviours the wxDataViewCtrl port left behind, both of which every list still on wxListCtrl inherits for free from CMuleListCtrl. Same class as the three restored in #796 (multi-selection, type-to-select, select-all) and the reason #801 argues for a shared base before the next list is ported.

Column show/hide menu

Right-clicking a column header opened a check-menu of columns (CMuleListCtrl::OnColumnRClick/OnMenuSelected). The ported search list bound no header right-click handler at all, so there was no way to hide a column.

Restored on CSearchListCtrl with the original semantics: hiding sets the column to COL_SIZE_MIN and caches the previous width, so re-showing restores what the user had, and the state persists through CListColumnStore's existing width handling instead of needing a second mechanism.

COL_SIZE_MIN moves from a file-local constant in MuleListCtrl.cpp to ListColumnStore.h, beside the column-width interface, so both lists read one threshold rather than keeping copies. It is 10 on wxGTK — which won't shrink a column past the header grip — and 0 elsewhere, so this touches the GTK build in particular.

Shift+page-up/down on macOS

Shift+page-up/down extends the selection on GTK and MSW, whose backends implement it. On macOS it does nothing: NSOutlineView pages the view without touching the selection. Handled by hand under __WXOSX__ so the three ports agree; repeated presses keep extending, since it grows the existing selection between the cursor's old and new position.

Plain page-up/down is deliberately left to the platform — macOS scrolls without moving the selection by convention (Finder, Mail) — and that behaviour is unchanged.

Shared ordering

Both the existing type-ahead search and the new page handler need the top-level rows in displayed order, so that is factored into BuildDisplayOrder() and shared rather than written twice. It runs the rows through this list's own comparator because GetItemByRow()/GetRowByItem() exist only in wx's generic implementation, not on GTK or macOS.

Testing

Built clean on macOS, Ubuntu 26.04 arm64 (wxGTK 3.2.9) and Windows 11 arm64; clang-format and both clang-tidy tiers clean on the diff.

Draft until the interactive pass on all three is done — specifically that a hidden column stays hidden across a restart, and that the macOS page size feels right.