Changes to RegressionVisualization 3D view and volume plot

I would like to request some small changes to the 3D view and volume plot:

- When the sequence is created and first displayed, center and zoom in on the shape
- Plot the regression volume as a solid line
- Change the default location of the legend, top-middle or bottom-middle preferably so as not to obstruct data
- Optional: Have the legend be draggable to any location in the plot

Start at the RegressionVisualization 3D view and volume plot entry points, then reproduce the sequence's first display to inspect the current framing, regression line, and legend placement. Done means the shape is centered and zoomed on initial display, the regression volume is a solid line, and the legend uses a non-obstructive default location; draggable legend behavior is optional.

Written by the indexing model from the issue text.