Consume normalized `ApiErrorDto` in remote functions

[a9ex]

Summary

Use the backend's normalized ApiErrorDto in frontend remotes instead of hardcoding error strings or falling back to generic 500 errors.

Motivation

The backend already returns a unified json { statusCode, error, message, issues? }.
Currently, the frontend ignores this DTO, duplicates hardcoded strings across switch (status) blocks, and swallows detailed backend errors behind a generic error(500, "An error occurred").

Proposed Solution

Add a helper to parse ApiErrorDto from the API response

Checklist

• I have searched for existing issues to avoid duplicates