Enhance simulation configuration and management features

- Added support for a `max_rounds` parameter in simulation API, allowing users to limit the number of simulation rounds, improving control over simulation duration.
- Updated README.md to reflect the new `max_rounds` parameter and its usage in simulation requests.
- Enhanced error handling for `max_rounds` input validation to ensure it is a positive integer.
- Modified simulation runner and related scripts to incorporate `max_rounds` functionality, ensuring consistent application across Twitter and Reddit simulations.
- Improved logging to indicate when the number of rounds is truncated due to the `max_rounds` setting, enhancing traceability during simulation execution.

backend/app/__init__.py

@@ -15,6 +15,11 @@ def create_app(config_class=Config):
     app = Flask(__name__)
     app.config.from_object(config_class)
     
+    # 设置JSON编码：确保中文直接显示（而不是 \uXXXX 格式）
+    # Flask >= 2.3 使用 app.json.ensure_ascii，旧版本使用 JSON_AS_ASCII 配置
+    if hasattr(app, 'json') and hasattr(app.json, 'ensure_ascii'):
+        app.json.ensure_ascii = False
+    
     # 设置日志
     logger = setup_logger('mirofish')