fix(label_list): emit reorder only after completed drops

[xy200303]

• I have read and agree to the CLA.

Summary

• fix the object list reorder signal so it only fires after a completed internal drop
• disable overwrite-mode drops in the object list to avoid replacing items when dropping onto another object
• add regression tests for non-drop removals and drag/drop configuration

Verification

• pytest -q tests/test_label_list_widget.py

Notes

• this addresses issue 在右侧列表拖动多个对象时会导致闪退 #1385 (在右侧列表拖动多个对象时会导致闪退)
• wider UI test imports are currently blocked in this environment by a pre-existing onnxruntime access violation during package initialization on Windows

[CVHub520]

Thanks for the contribution. After testing this, we decided not to move forward with the PR.

The current drag-reordering behavior can introduce data-loss risks: dragging items in the Shapes list may cause some objects to disappear from both the list and the canvas. Also, this reordering feature has limited practical value for the current annotation workflow, so keeping it would add interaction risk without enough benefit.

We’ll close this PR and disable shape-list dragging for now.

#1385