Enhancement: WPF tray context menu (Phase 2)

## Problem
Phase 1 health coalescing (#8) fixed most tray menu stalls. If menu remains sticky, migrate WinForms `ContextMenuStrip` to WPF `ContextMenu`.

## Acceptance criteria
- [ ] Only implement if Phase 1 insufficient in production use
- [ ] Menu responsive during heavy builds
- [ ] Exit and dismiss behave reliably

## Surfaces
TrayApp

## Related
#8 (Done)