Per-marker UI hint (milliseconds, ge=1) for how long the Web UI keeps a
marker highlighted after a match. Mirrors color: stored on the link,
persisted in the topology, inherited via project-level definitions, and
never sent to uBridge. Omitted = null = frontend uses its own default.
The default is intentionally NOT set in the schema: MarkerCreate also
backs PUT updates, so a schema default would make every partial update
silently reset the value. None means "not provided" (keep existing on
update / frontend decides on create).