Add ability to disable fit to frame on expansion

When expanding a node, the graph will perform a "fit to frame" operation at the end that will zoom in or out to recenter and fit the entire graph in the frame.

This is not always desired and can be a bit frustrating.

## Potential solutions

- Add app-wide setting to disable or enable this feature
- Add session-wide setting to disable or enable this feature

This could potentially be a toggle in either the global app settings page and apply to all sessions, or it could be a toggle that is always available within the graph view (perhaps in the toolbar).

Choosing the right location will depend on how often the setting is changed. There is no need to devote screen real estate to it on the graph view if the user turns it off once and never touches it again.

## Related issues

- #316
- #888

Start by tracing the graph-view flow that runs fit to frame after a node expands, then compare the global app settings, session settings, and graph toolbar options described in the issue. Review related issues #316 and #888 before deciding where the toggle belongs; done means users can disable or enable the post-expansion fit-to-frame behavior at the chosen scope.

Written by the indexing model from the issue text.