fix(Sync): Display errors on sync branches modal

[gatzjames]

Currently errors are not displayed properly inside the modal for syncing branches.

Highlights:

• Adds proper error handling

Next steps:

• Move the branches modal functionality in the sidebar to improve UX as alerts on top of a modal are creating a lot of friction

Closes INS-3850

[jackkav]

this use effect idle checker pattern is smelly and error prone, is there any hope of something better?

[gatzjames]

this use effect idle checker pattern is smelly and error prone, is there any hope of something better?

React 19/router v7 will have the new actions api which will remove all this dependency management. Currently not sure if there's a better approach