- Extend canvas store addNode's auto-overlap avoidance (ring-scan) to all
node types, not just 'image'. Previously, repeated import-to-canvas for
world3d/model3d nodes stacked them on the same viewport center
coordinate, making them appear locked and impossible to drag apart.
- Add addNodesBulk helper that loops addNode and reuses its avoidance
logic, suitable for batch-importing multiple history records.
- Wire selectedAddTaskIds state, addableTasks/selectedAddTasks memos,
toggle/selectAll handlers, and prepare handleBatchImportToCanvas in
the3D canvas page so future UI can hand off bulk import to the store.
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