List projects available for Cloud Connect attachment

Returns every project the authenticated caller may attach an enrolled Cloud Connect instance to. Policy is evaluated entirely by the server: today, results include only live, unattached standalone projects in the resolved organization, and user credentials require that organization's owner or admin role. Exactly one organization is searched per request and the response names it in org, so an empty projects states which organization has no eligible project rather than leaving a client to wonder whether the one it meant was searched at all; name another with X-Org-Name. Clients must render every returned project and instance without applying their own eligibility filters. The instances array is part of the stable contract and may be populated when server policy permits projects with existing attachments.