mark/flag agent #50

fix: keep rapid agent mark toggles from repeating themselves

test: cover the immediate repaint after an agent mark toggle

fix: keep the machine initial when a collapsed agent row is marked

fix: restore the agent mark projection when the server refuses it

fix: bold the collapsed mark so a colliding color stays readable

fix: default the agent mark color to magenta

fix: base the agent mark rollback on the server-confirmed value

fix: show agent marks in the default collapsed sidebar and CLI help

fix: keep in-flight agent marks across snapshots and repaint refusals

test: pin the shared mark baseline across two failing requests

fix: let a newer server mark win over an in-flight optimistic one

fix: publish a pane update when an agent mark changes