consider supporting harmonization in original image space

e.g. pulling back harmonization parameters like the $\gamma,\delta$ images from ComBat back to the original image space along the deformation that registered images to the template

we need to think about whether this fits with the role of HABET and where

The issue names no files, tests, or entry points. Start by reviewing how HABET handles image registration and ComBat harmonization, then clarify whether pulling parameters back to original image space fits HABET's role. Done requires an agreed scope and behavior for the deformation-based parameter mapping.

Written by the indexing model from the issue text.