- Fix Viz3D exports to include flow visualization functions
- Export setFlowLayerVisible, setDwellLayerVisible, setCorridorLayerVisible
- Export setFlowTimeFilter, setFlowData, setDwellData, setCorridorData
- Remove duplicate setDwellLayerVisible function definition
This completes the crowd flow visualization feature that was
already implemented in the backend (flow.go) and frontend
(crowdflow.js, viz3d.js) but had missing exports in the Viz3D module.
