feat(t214): persist candidate observation identities

backend-api/internal/domain/task.go

@@ -168,6 +168,19 @@ type CandidateObservation struct {
 	EvidenceAssetIDs []string
 	CollectionStatus string
 	ObservedAt       time.Time
+	Identity         *CandidateObservationIdentity
+}
+
+type CandidateObservationIdentity struct {
+	CandidateKey                string
+	ExecutionID                 string
+	CandidateOrdinal            int
+	CardSignature               string
+	DetailSignature             string
+	DetailEvidenceSHA256        string
+	SpecificationEvidenceSHA256 string
+	IdentityVersion             int
+	CreatedAt                   time.Time
 }
 
 type CandidateModelRun struct {