feat: Add self-use mode for model ratio and price configuration

- Introduce `SelfUseModeEnabled` setting to allow flexible model ratio configuration
- Update error handling to provide more informative messages when model ratios are not set
- Modify pricing and relay logic to support self-use mode
- Add UI toggle for enabling self-use mode in operation settings
- Implement fallback mechanism for model ratios when self-use mode is enabled

web/src/components/OperationSetting.js

@@ -60,6 +60,7 @@ const OperationSetting = () => {
     RetryTimes: 0,
     Chats: "[]",
     DemoSiteEnabled: false,
+    SelfUseModeEnabled: false,
     AutomaticDisableKeywords: '',
   });