CngxTimelineMarkerHost

The contract a timeline exposes to the rows beneath it, so an app-wide marker template can reach a dot the organism does not itself render.

<cngx-timeline> is data-driven in v1: the consumer owns the whole row template and writes <cngx-timeline-item> themselves, which means the organism has no handle on the marker inside it. Passing the resolved template through DI is what closes that gap without the row having to thread it down by hand.