Coverage Preview Endpoint

Staged coverage for a customer-supplied package list, before signup: for each package, whether it is recognized, has a linked repository, has recent activity data, has an open forecast, and has a validated (not withheld) track record -- with the reason spelled out at whichever stage a package falls short, rather than omitted. packages is a comma-separated list, each entry in the same form /v1/risk accepts, optionally as name@version or a package URL (the version is quoted back as typed, never assessed). Duplicates are dropped by the full typed entry, so x@1 and x are two entries. Unmatched entries are reported, never silently dropped, and a name that exists in more than one ecosystem is listed under ambiguous with the resolver's own message rather than failing the request. See foresight_api.coverage_preview for the stage definitions.