Improvements and bugfixes

To initiate a new Studio without installing the CLI globally:

npm create sanity@latest

To upgrade a v3 Studio, run this command in its folder:

npm install sanity@latest

• Responsive improvements to the Vision plugin to accommodate narrower screens
• Updated icon for copy buttons
• Bump engines.node to >= 18

Fixes type for canHandleIntent to allow passing undefined

Fixes placement of "Add item…" popover in array inputs

Fixes a bug where edit intent was not called when added to a menuItem (thanks @israelroldan 🙏)