Improve feedback on invalid form submission

Currently, when a user attempts to submit an invalid form, the submission API call is bypassed and nothing happens. There is no feedback to the user that they need to check their fields for valid entry.

There should be some UI feedback if a submission is not completed after `Submit` is clicked.

No files or tests are named. Start by tracing the Angular form submission handler and its validation path; confirm how invalid submissions currently bypass the API call. Done means clicking Submit on invalid input produces visible UI feedback directing the user to check the fields.

Written by the indexing model from the issue text.