[UX] Misc small bugs

- [ ] Shift selection in Smart Script doesn't work
- [ ] When you have selected multiple actions, and you click an action to drag, it is unselected [PRIORITY]

- [x] In Packet Viewer: when completion box pops out, and then it is closed, it is still opened but 'ENTER' key is not working as it should
- [x] In packet Viewer: go to packet id

Start by reproducing the two unchecked behaviors in the Smart Script editor: Shift selection and dragging a selected action. The issue names no files or tests, so locate the relevant UI entry points first; done means range selection works and dragging an action preserves the existing multi-selection.

Written by the indexing model from the issue text.