Add dragging/deletion/automatic camera focus shift function on electrons in 3d

[Yukieos]

Description:
Current version: I write a long list of predefined coordinates, and each click of the + and - buttons simply adds an electron from this list to the screen.
To do: Similar to the 2D folders, I want the electrons to be added randomly, and users can drag these electrons on the screen to see the change of the direction of the electric field in the 3D version.

The key goals are:

1. Dragging ✅
   -Can drag any existing charge to reposition it in real time.
   -Update the corresponding charges[i].position and refresh the field lines.

2. Deletion✅
   Add a feature that double-clicking a charge can remove it

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Planned finish time: next week;
Feel free to comment or suggest any changes to the plan!