Group 1 of the task-row context menu gets a fourth gated entry, right
after "Open interactive session": it opens the task's worktree folder
via Process.Start/UseShellExecute, mirroring ListsIslandViewModel's
OpenInExplorer. Missing worktree greys the item out with a tooltip
reason instead of hiding it, keeping Group 1's fixed length. Failures
report through TasksIslandViewModel.ErrorReported (footer strip), not
a silent catch.