pause/resume was fire-and-forget: the controller sent marker pause/resume but
stored nothing, so the Web UI could only keep a local optimistic flag that was
lost on panel reopen. Treat the mute as a project-level config (like per-marker
enabled): record _markers_paused, persist it in the topology (asdict + load),
and echo it on the project object so the UI renders from server truth.
Because marker pause is a uBridge runtime flag that resets on node restart,
start_all re-applies the mute to freshly started uBridges after a project
reopen — a paused project stays paused across close/reopen.