feat: load explicit configuration references and remove implicit env overlays

cmd/go-omni/apigen/testdata/managed/consumer_test.go

@@ -123,7 +123,7 @@ func TestGeneratedTransfers(t *testing.T) {
 func configFile(t *testing.T, address string, fail bool) string {
 	t.Helper()
 	path := filepath.Join(t.TempDir(), "config.json")
-	data, _ := json.Marshal(map[string]any{"server": map[string]any{"address": address}, "failInit": fail})
+	data, _ := json.Marshal(map[string]any{"server": map[string]any{"address": address, "transport": "${GO_OMNI_TRANSPORT:-nethttp}"}, "failInit": fail})
 	if err := os.WriteFile(path, data, 0600); err != nil {
 		t.Fatal(err)
 	}