Add render artifact model, config, and Seriatim adapter contracts

internal/config/validate.go

@@ -88,6 +88,9 @@ func validatePipeline(cfg *PipelineConfig) error {
 	if err := validateTrim(cfg.Trim); err != nil {
 		return err
 	}
+	if err := validateRender(cfg.Render); err != nil {
+		return err
+	}
 	if err := validateScriptorium(cfg.Scriptorium); err != nil {
 		return err
 	}
@@ -299,6 +302,26 @@ func validateTrim(cfg *TrimConfig) error {
 	return nil
 }
 
+func validateRender(cfg *RenderConfig) error {
+	if cfg == nil {
+		return nil
+	}
+	if cfg.Enabled == nil {
+		return fmt.Errorf("pipeline.render.enabled must be set (defaults should populate this)")
+	}
+	if cfg.IncludeTimestamps == nil {
+		return fmt.Errorf("pipeline.render.include_timestamps must be set (defaults should populate this)")
+	}
+	format := strings.TrimSpace(cfg.Format)
+	if format != "markdown" {
+		return fmt.Errorf("pipeline.render.format must be markdown")
+	}
+	if cfg.Title != "" && strings.TrimSpace(cfg.Title) == "" {
+		return fmt.Errorf("pipeline.render.title must be non-empty when provided")
+	}
+	return nil
+}
+
 func validateWhisperX(cfg WhisperXConfig) error {
 	if strings.TrimSpace(cfg.TranscribeURL) == "" {
 		return fmt.Errorf("pipeline.whisperx.transcribe_url is required")