Add undo and redo ops to the headless server (synchronous via update()).
Combined with select, the modify commands MOVE/COPY work through the
existing dispatcher — "select type=Line" then run("MOVE 0,0 10,0")
translates the selection. ocs.py gains undo()/redo().
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>