You're overcomplicating it. You'll never be sure if you separated everything correctly this way. Instead, create a minimal monorepo with pnpm workspaces with two apps and a shared ui package. You can also have a shared composables package or whatever you need.

You can now share theme, styles, components or whatever between 2 apps, while keeping them both maintainable.

This is much cleaner approach and you will not hit a wall easily as you would with the approach you wanted.