Diagram Tier

Declared ON A CLASS — the semantic-zoom tier ("chip"/"icon"/"card"/"full") its instances render at when they appear as NODES in a tile-based diagram (cluster / connector / DAG). A facet's own `nodeTier` overrides it; absent both, nodes default to icon. Lets a type set its own at-rest detail level without each diagram repeating it. (The modal's scroll-zoom still escalates tiers live, independent of this.)