feat: Add user notification settings with quota warning and multiple notification methods

- Implement user notification settings with email and webhook options
- Add new user settings for quota warning threshold and notification preferences
- Create backend API and database support for user notification configuration
- Enhance frontend personal settings with notification configuration UI
- Support custom notification email and webhook URL
- Add service layer for sending user notifications

setting/system_setting.go

@@ -0,0 +1,9 @@
+package setting
+
+var ServerAddress = "http://localhost:3000"
+var WorkerUrl = ""
+var WorkerValidKey = ""
+
+func EnableWorker() bool {
+	return WorkerUrl != ""
+}