feat(journey/settings): warn on unsaved changes before closing modal

- Track dirty state (title/subtitle changed from original)
- Intercept X button, backdrop click, and Cancel with handleClose
- Show ConfirmDialog when dirty; proceed with onClose only on confirm
- Add common.discardChanges and common.discard keys to all 15 locales

client/src/i18n/translations/zh.ts

@@ -30,6 +30,8 @@ const zh: Record<string, string> = {
   'common.none': '无',
   'common.date': '日期',
   'common.rename': '重命名',
+  'common.discardChanges': '放弃更改',
+  'common.discard': '放弃',
   'common.name': '名称',
   'common.email': '邮箱',
   'common.password': '密码',