ScriptBehavior gains App() host access (Application injected via
ScriptRuntime), TryGet<T> and EntityBits for physics facade addressing.
WASDMove maps WASD to the editor camera's horizontal heading (UE
gameplay convention): dynamic bodies go through the physics velocity
facade preserving the vertical component (zeroing Y would cancel
gravity mid-fall), bodiless entities translate their transform directly.
Editor-mode key conflict is naturally avoided: RMB-held flight consumes
WASD, release hands keys to the script.
