FSkinWeightBrushConfig

For saving/restoring the brush settings separately for each brush mode (Add, Replace, etc...) Note: Radius and FalloffMode are stored per-mode for serialization compatibility, but at runtime they behave as shared values — every writer propagates to all four per-mode configs (see USkinWeightsPaintToolProperties::SetSharedRadius / SetSharedFalloffMode) and RestoreProperties forces all four entries into sync on load.