Rebuild interactive features removed in AIDA

Several interactive features (click_center, interactive marking) were dropped from the image display API because the belong to the viewer not to the display of an image. Two to-dos here: make a list of the features that no longer work, and come up with a plan to implement them.

Start by reviewing the image display API and viewer boundary described in the issue. Inventory which interactive features, including click_center and interactive marking, no longer work after AIDA, then document a plan for restoring them in the viewer. Done means the missing-feature list and an agreed implementation plan are recorded.

Written by the indexing model from the issue text.