♻️ refactor(ui): create `Header` component in UI

[tnyo43]

Context

Header components are defined in the app (Header) and erd-core (AppBar) packages independently.

Problem

It causes several issues:

• The Toast component from the ui package implicitly depends on the Header styles
• A z-index custom property for Header component is defined in the ui package

Proposed Solution

We should define a common Header component in the ui and make the application headers depends on it.

Reference

#2943 (comment)

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.