Three fixes:
1. interaction/index.ts: Add layerId to created element in confirmDraw()
2. CanvasArea.tsx: Sync layers to LayerManager via layerManagerRef
3. App.tsx: Fallback to activeLayerId in handleElementCreated if layerId missing
Root cause: LayerManager.activeLayerId was empty because layers were never
synced from React state to the interaction layer LayerManager. New elements
got layer_id="" which failed SQLite FOREIGN KEY constraint.
Also includes Yjs sync race condition fix from previous commit.
Leopoldadmin