Don't allow users to directly edit date string, only allow widget date selection

We have a single case, reported by Marjo, of a residency with an "invalid" date. The date can not be edited to fix the issue, as this has previously led to more widespread issues with residency management.

We need to tread cautiously here, to avoid "painting ourselves into a corner" while figuring out how to reduce the likelihood of user errors with
- creating/modifying residencies
- entering dates

Discuss with Marjo how to approach these situations and implement the desired solution, while acknowledging trade-offs and development costs.