[1.15.0] Transcription: embedded modal must be a div, not a dialog

Problem/Motivation

🐛 Remplace la balise dialog par une balise div, le rôle dialog est ajouté automatiquement à l'ouverture de la modale #1478

Upstream keeps <dialog> for regular modals but the transcription's embedded modal is now <div class="fr-modal"> (role set by JS on open). Our transcription.twig composes ui_suite_dsfr:modal, which hardcodes <dialog> with role/aria-modal.

Proposed resolution

We could add a tag prop to the modal component (dialog by default) that also drops role/aria-modal when set to div, and use it from transcription.

The modal title part (#1465) is already fine, transcription already passes a title to the modal.