The API ships {error: "<code>"} envelopes (e.g. "course_not_found"); we
were displaying that raw, or worse, "[object Object]" when callers tried
to print the payload. Map the 16 known codes (catalogued from the
delivery API routes) to human strings, prefer the optional `message`
field on auth routes, and fall back to a mentor-facing message for
unknown codes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
psmyrdek