Register the @querystringSearch route

[sneridagh]

The Querystring widget fetches its results preview from /@querystringSearch. The loader exists in packages/cmsui/routes/querystringSearch.tsx, but the route was never registered in packages/cmsui/config/routes.ts. Requests fell through to the publicui * content route, the root middleware called getContent('/@querystringSearch'), and the response was a 404.

Changes

• Register @querystringSearch as a prefix route, like @queryStringOptions.
• Add an acceptance test that requests the route as a logged-in editor and checks it returns the matching content as JSON. Both tests fail with a 404 without the fix.
• Add a news fragment.

Notes

• No form on main renders the Querystring widget yet, because the Listing block has no settings schema. That arrives with listing block #107, which contains the same route registration, so the test exercises the route directly instead of the UI preview.
• After Let resource routes skip the root content middleware #265, @ resource routes skip the root content middleware by default. This route only uses ploneClientContext, so it needs no skipContent flag.
• When listing block #107 rebases, its loader expects ?query= to be the full querystring object, while this test sends the bare criteria array. The test will need to follow.