Create a dedicated Mutational Report

It is time we created a dedicated HTML phase report

The report should be:
* Title should include the execution mode.
* There should be an entry per scenario.
* Each scenario is expandable
* When expanded there will be one line per shuffle group
* If we have mutiple events we have an expandable table per event.

Start by locating the existing phase-reporting entry points and any current HTML output. Compare their behavior with the requested execution-mode title, scenario and shuffle-group structure, and expandable event tables. Done means a dedicated HTML report satisfies each listed requirement and is covered by the project's relevant tests.

Written by the indexing model from the issue text.