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/en.ts

@@ -30,6 +30,8 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'common.none': 'None',
   'common.date': 'Date',
   'common.rename': 'Rename',
+  'common.discardChanges': 'Discard Changes',
+  'common.discard': 'Discard',
   'common.name': 'Name',
   'common.email': 'Email',
   'common.password': 'Password',