Simplify downstream tool configuration

internal/config/validate.go

@@ -276,9 +276,6 @@ func validateAudita(cfg AuditaConfig) error {
 			return fmt.Errorf("pipeline.audita.base_url must be a valid URL")
 		}
 	}
-	if strings.TrimSpace(cfg.Model) == "" {
-		return fmt.Errorf("pipeline.audita.model is required")
-	}
 	if cfg.TotalLLMConcurrency != nil && *cfg.TotalLLMConcurrency <= 0 {
 		return fmt.Errorf("pipeline.audita.total_llm_concurrency must be > 0")
 	}