Generate the mainframe findings report

Write everything the mainframe analyses found wrong as a ranked markdown report, grouped by severity and category, each finding carrying the evidence it was derived from and the file it is in. Rules that can never fire and paragraphs nothing reaches come first; redundant rules and leftover exit paragraphs come last, counted rather than allowed to crowd out the rest.

This recipe reads the Findings data table that the mainframe analyses populate, so it produces nothing on its own. Run it as part of io.moderne.mainframe.prethink.UpdateMainframePrethinkContext.