test(storage): cover ServerConfig.AuthBroker in saveServerSync field canary

AuthBroker (spec 074) is server-edition per-upstream broker config carried
in the JSON config (like Shared), not persisted to the BBolt UpstreamRecord.
Mark it intentionally excluded in TestSaveServerSyncFieldCoverage so the
field-coverage canary passes.

Related #588

Author: Dumbris

internal/storage/async_ops_test.go

@@ -252,6 +252,9 @@ func TestSaveServerSyncFieldCoverage(t *testing.T) {
 		// (and the custom-origin skip_quarantine guard) survive a restart.
 		"SourceRegistryID":         true,
 		"SourceRegistryProvenance": true,
+		// Spec 074: server-edition per-upstream broker config; lives in the JSON
+		// config (like Shared), not persisted to the BBolt UpstreamRecord.
+		"AuthBroker": true,
 	}
 
 	// Get all fields from ServerConfig
@@ -287,6 +290,10 @@ func TestSaveServerSyncFieldCoverage(t *testing.T) {
 			// Spec 032: runtime-only field, not persisted to BBolt
 			continue
 		}
+		if fieldName == "AuthBroker" {
+			// Spec 074: server-edition JSON-config field, not persisted to BBolt
+			continue
+		}
 		if !upstreamFields[fieldName] {
 			t.Errorf("Expected field %q in UpstreamRecord but not found", fieldName)
 		}