Import: suporte a import de candidatas apenas com e-mail

Critérios
====
- [ ] Fazer validação do email da candidata na planilha, ao fazer a importação da mesma

No files, tests, or entry points are named. Start by locating the candidate spreadsheet import flow and its email-handling logic, then identify the existing validation conventions. Done means imports accept candidates using only a valid email and reject or report rows with invalid email data.

索引モデルが issue の本文から書いたものです。