Feat/LOY-158 signup with existing email error handling
* feat(LOY-158): Add handling for email conflict during signup
- Implement specific error handling for email conflict in signup form
- Add localized error message for existing email accounts across language dictionaries
- Introduce new error type `conflictError` in trpc error handling
* fix(LOY-158): revert translation changes
* fix(LOY-158): Correct Finnish translation for cancellation message
Approved-by: Christian Andolf