[NGO Admin/ Cazuri] Field "Data nasterii" causes Err 500 at add beneficiary or edit

https://github.com/user-attachments/assets/a08a1848-3c3e-49cd-865b-9934e32ac6e6

Start by reviewing the linked screenshot and reproducing the error when adding or editing a beneficiary with the “Data nasterii” field. Trace the resulting HTTP 500 response to identify the failing entry point; done means both beneficiary flows accept or correctly validate this field without a server error.

Written by the indexing model from the issue text.