Vuestic landing

Right now vuestic-admin is pretty much a project boilerplate encased in repository.

But landing is selling page for vuestic-admin itself. So it's great idea to separate them. We still want to keep Vuestic landing open source, so that users can use it to create similar landings or observe best practices.

* [Design](https://www.figma.com/file/1FrFtIjHjMAV0o4t0wpYGq/Admin?type=design&node-id=1086-1010&mode=design&t=dFtptu8MWHzhcgeE-0)

## Other
* We want to reuse vuestic ui docs project as much as possible. Most of the design from vuestic landing page is taken for admin design.
* Keep placeholders for documentation pages. At first - we don't need any pages, but at engine level these will be needed somewhere in the future (i.e. you can leave several pages in docs, but no navigation from admin page, so you would be able to only go there by url).
* We would need to change domain. `admin.vuestic.dev` - would go to landing. `admin-demo.vuestic.dev` - to admin project itself (currently admin.vuestic.dev). We can do this after implementation.
* Bonus points for abstracting away (maybe using as a dependency) vuestic docs logic that's common across ui and admin docs.
* We want to move analytics (tag manager) from vuestic admin here. Demo should have no analytics.

Start with the linked Figma design and compare the existing vuestic-admin landing, admin project, and Vuestic UI docs. Define the separation so the landing remains open source, documentation placeholders are available, analytics move to the landing, and the demo has no analytics; domain changes are explicitly deferred.

Written by the indexing model from the issue text.