Working towards sippy-chat AI analysis of regressions, we need a /regressions endpoint, as well as a way for external callers to construct test_details links. A good rest API should provide those hateoas style links. For this card, for each regressed test, include a link to the API call for the test_details report.

The JS UI code will no longer have to do this itself, and other callers of the report can now walk to the test details links.