Move generated file writes into owning adapters

internal/adapters/seriatim/generated_config.go

@@ -0,0 +1,19 @@
+package seriatim
+
+import (
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/fileops"
+	"gopkg.in/yaml.v3"
+)
+
+func writeGeneratedYAML(path string, payload any) error {
+	data, err := yaml.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal generated YAML for %q: %w", path, err)
+	}
+	if err := fileops.WriteFileAtomic(path, data, fileops.WorkspaceFileMode); err != nil {
+		return fmt.Errorf("write generated YAML %q: %w", path, err)
+	}
+	return nil
+}