Add server-side validation in BulkRequestSignatures, RequestSignature, and RequestApproval to load the referenced profiles and verify none have an ended contract before proceeding. Returns ErrProfileContractEnded if a profile's contract_end_date is in the past, surfaced as a CONFLICT GraphQL error in all three resolvers. Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>