Consistent modal IDs across React Elements

🔍 Problem Statement

As a developer, Pelcro React Elements modals lack consistent IDs, making customization and DOM targeting unreliable.

💡 User Story

As a developer, I want every modal to have a predictable, consistently-named DOM ID so I can reliably target, style, and instrument it.

🎯 Definition of Done (DoD)

1. ✔ Given any Pelcro React Elements modal, when it mounts, then its root element has a stable id following the agreed naming convention (e.g. pelcro-modal-{name}).

2. ✔ This change will impact UI, specifically the ReactJS Elements library.

3. ✔ Limitations: modal root IDs only; nested elements are out of scope. Naming convention must be published in the Elements docs.