Testing checklist

Method	Path	Description
GET	.../testing-checklist	Every item on the session's checklist.
POST	.../testing-checklist/generate	Generate or refresh items from the branch-only diff.
PATCH	.../testing-checklist/{itemId}	Set a result. Body { result }, one of pass, fail, null.
DELETE	.../testing-checklist/{itemId}	Remove an item.