Sub-issue of #43. After submitting an invalid form, "Please correct the highlighted fields" stays visible even when every field has been fixed. Fixed fields keep an `undefined` entry in the errors object, and the summary counts keys instead of actual errors. ## Tasks - [ ] Show the summary only when at least one field has an error - [ ] Make the "removes the error summary once every highlighted field is fixed" test pass ## Done when - [ ] The summary disappears as soon as no field is marked invalid