MigrationDocKind: "Actor" | "Item" | "ActiveEffect" | "RegionBehavior" | "Scene"

The document classes a migration can target. These are Foundry document-class names (not SoHL subtypes) used as the dispatch key for a step's per-type migrators. The SoHL in-scope types map onto them as: Actors (being/cohort/structure/vehicle) → Actor; the 13 item subtypes → Item; the sohleffectdata effect → ActiveEffect; the trigger region behavior → RegionBehavior. Scene is included so a future migration can touch scene-level flags even though Scenes carry no SoHL system data.