Revert: use text output format instead of JSON

- Remove --output-format json from CLI commands
- Change output filenames from output-{N}.json back to stdout-{N}.txt
- Keep outputs in outputs/ subdirectory for clean structure

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

integration-tests/concurrent-runner/runner.py

@@ -588,7 +588,7 @@ class QwenRunner:
             self.console.print(f"[dim]Command: {' '.join(cmd)}[/dim]")
 
             # Prepare output files for this prompt
-            stdout_file = outputs_subdir / f"output-{prompt_index}.json"
+            stdout_file = outputs_subdir / f"stdout-{prompt_index}.txt"
             stderr_file = outputs_subdir / f"stderr-{prompt_index}.txt"
 
             # Run the CLI
@@ -655,9 +655,6 @@ class QwenRunner:
         if self.config.yolo:
             cmd.append("--yolo")
 
-        # Use JSON output format
-        cmd.extend(["--output-format", "json"])
-
         # Always enable OpenAI logging to run-specific logs directory
         cmd.append("--openai-logging")
         cmd.extend(["--openai-logging-dir", run.logs_dir])