refs https://github.com/TryGhost/Product/issues/4152
---
<!-- Leave the line below if you'd like GitHub Copilot to generate a
summary from your commit -->
<!--
copilot:summary
-->
### <samp>🤖[[deprecated]](https://githubnext.com/copilot-for-prs-sunset)
Generated by Copilot at a28462f</samp>
This pull request adds a new admin-x app called `admin-x-demo`, which
demonstrates how to use the shared packages `admin-x-framework` and
`admin-x-design-system` to create a simple app that renders a button and
a modal. It also improves the development workflow, the vite
integration, the dependency management, and the type checking for the
admin-x apps and packages. It modifies some files in the
`admin-x-framework` and `admin-x-design-system` packages to make the
modals prop optional, to introduce a new type for the props from the
Ember app, to fix the z-index of the modal backdrop, and to use
consistent file extensions and module syntax.
refs https://github.com/TryGhost/Product/issues/4123
---
<!-- Leave the line below if you'd like GitHub Copilot to generate a
summary from your commit -->
<!--
copilot:summary
-->
### <samp>🤖 Generated by Copilot at a420f0b</samp>
This pull request moves most of the API-related types and functions from
the `admin-x-settings` package to the `admin-x-framework` package, which
is a new library of common utilities and hooks for the admin-x apps. It
also adds some configuration files, such as `.eslintrc.cjs` and
`.gitignore`, to the `admin-x-framework` package. Additionally, it
exports the `FetchKoenigLexical` type from the `admin-x-design-system`
package, which is used by the `HtmlEditor` component.
