Honest copy for server-side image-upload failures (practicas/nueva)

appEvents a69fe472 (2026-08-17): UND_ERR_CONNECT_TIMEOUT from the Vercel function to api.pensanta.com surfaced to the student as 'Verificá tu conexión y el tamaño de los archivos' - blames the user's connection for a server-side upstream failure. Fix: isServerSideImageFailure() in src/lib/image-api.ts (non-ImageApiError = api-images never answered = server-side class); practicas/nueva upload catch now shows 'No pudimos guardar las imágenes por un problema temporal del servidor. Probá de nuevo en un momento.' for that class, keeps the file-shaped copy when api-images answered with a code. detail.userMessage records whichever string was shown. mi-cursada/editar path already has neutral copy (Intentá de nuevo) - untouched.