Highlight both incoming and outgoing links when hovering over a node

I think it would be useful if dependo could highlight both incoming and outgoing links when hovering over a node. Right now it only highlights the outgoing links.

Maybe holding down different modifier keys (alt, ctrl) while hovering could hide one or the other sets.

Start by tracing the graph report's existing node-hover behavior, which currently highlights only outgoing links. Clarify whether modifier keys should independently hide incoming or outgoing links, then verify that hovering highlights both link directions and that any agreed modifier behavior works consistently.

Written by the indexing model from the issue text.