fix: persist execution.dryrun setting and add headless mode option for User

- Add EXECUTION_DRYRUN to save_to_env() to fix dryrun setting not persisting
  after restart
- Add headless mode checkbox in User mode settings for browser visibility control

Co-Authored-By: Claude (glm-5) <noreply@anthropic.com>

config/loader.py

@@ -162,6 +162,8 @@ class ConfigLoader:
             "VALIDATION_ENABLE_CRUD": config.validation.enable_crud_operations,
             "VALIDATION_DEFAULT_MANAGER": config.validation.default_manager,
             "VALIDATION_MATCH_MODE": config.validation.match_mode,
+            # 执行配置
+            "EXECUTION_DRYRUN": config.execution.dryrun,
         }
 
         return save_env_file(env_file, env_dict)