fix: delete reverse-selected rows with demo

[fangsmile]

Summary

• Includes PR fix: delete reverse-selected rows correctly #5225 changes for issue [Bug] #5214.
• Adds a browser demo to reproduce and verify deleting rows selected by dragging upward.

Demo

• packages/vtable-plugins/demo/context-menu/issue-5214-reverse-selected-row-delete.ts
• Open vtable-plugins demo and select issue-5214-reverse-selected-row-delete.
• Click "模拟反向选区并右键删除"; fixed behavior shows PASS and records=[0,4].

Validation

• Browser interaction verified locally with Chrome DevTools MCP: PASS | records=[0,4]
• @visactor/vtable-plugins compile passed.

Review note

• The included original changeset currently targets @visactor/vtable with type none, while the production changes are in @visactor/vtable-plugins. This should be adjusted before final merge.