Merge polecat/dementus-mkddymu6: Improves KillSessionWithProcesses to
recursively find and kill all descendant processes, not just direct
children. This prevents orphaned Claude processes when the process
tree is deeper than one level.
Adds getAllDescendants() helper and TestGetAllDescendants test.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>