Description

gql() in frontend/src/api/graphql.ts calls await res.json() without
checking res.ok first. If the server returns a 401/500 with an HTML error
page, res.json() throws an opaque SyntaxError instead of a useful API error.

Fix

• Read response as text first, then attempt JSON.parse in a try/catch
• Check res.ok before accessing response data
• Surface HTTP status and body preview in thrown errors

Frontend-only change. File affected: frontend/src/api/graphql.ts