ArchitectureDiffReporter

Renders an ArchitectureDiff as a pull-request comment.

Architecture changes are invisible in a normal diff: adding one line to a dependencies { } block can wire two subsystems together, and the review shows one line. This turns that into a paragraph a reviewer reads without knowing the graph.

Ordered by consequence rather than by kind - a new cycle first, then dependencies, then modules - because a reviewer skims from the top and the first thing they see should be the thing most worth their attention.