Disk picker dialog doesn't scale: add scroll, resizable columns, sort + search

[relmer]

Summary

The boot / Insert-Disk picker (AssetBootstrap::PromptBootDiskMru and PromptInsertDiskMru, rendered through a DialogPrimitive custom body hosting a DxuiListView) does not scale to large lists or long text. It was built for a handful of rows (a few MRU entries + 2 stock downloads). This is now much easier to hit since the picker also lists in-repo Apple2/Demos disks (7) alongside recents and downloads.

Problems (investigated 2026-06-26)

No scroll — dialog grows off-screen.

• onMeasureCustomBody returns GetTotalMeasuredWidthPx() × GetRequiredHeightPx() — both auto-fit to content, unbounded. GetRequiredHeightPx() = header + rows × rowHeight (DxuiListView.cpp:1027).
• DialogPrimitive::GetInitialWindowRect clamps only the dialog's position to the monitor work area, not its size (DialogPrimitive.cpp:1560-1561). A long list grows the dialog taller than the screen, pins it to the top, and pushes the bottom rows and the Skip/Cancel/Browse buttons off-screen, unreachable.

Custom-body input channel cannot scroll.

• DialogInputEvent::Kind = { MouseMove, LeftButtonDown, LeftButtonUp, KeyDown } — there is no wheel kind. The picker's onInputCustomBody only handles MouseMove + LeftButtonUp.
• DxuiListView is fully scrollable (ScrollByWheelDelta, scrollbar hit-tests, keyboard) but is never given a bounded rect, nor any wheel/scrollbar/keyboard input.

Columns not resizable and overgrow.

• MeasureColumnsPx auto-fits every column, including the stretch "Location" column, to its widest cell (DxuiListView.cpp:350-361). A long path grows the dialog wide, spilling off the right edge (again only position-clamped).
• DxuiListView supports divider resize (mouse HitTestColumnResize + keyboard m_focusedDividerCol / Left-Right) but the picker forwards none of it. No truncation fallback either.

Wanted

1. Scroll — clamp the dialog body to the monitor work area; hand DxuiListView a bounded rect so it enters scroll mode (it already renders a scrollbar via ScrollbarMetrics).
2. Wheel/scroll input — add a Wheel kind (+ wheelDelta) to DialogInputEvent and forward wheel / scrollbar-click / keyboard from the custom-body channel to the list.
3. Resizable columns — cap column widths with truncation; optionally wire divider-resize input through the dialog.
4. Sort — wire header-click column sort (DxuiListView::SetSortIndicator already exists).
5. Search — add a filter box to narrow rows by name/path substring.

This likely needs a DialogPrimitive custom-body input extension (wheel + capture), since this picker and future custom-body dialogs hit the same channel.