The API moved to mathapi.tadrisino2.ir on 2026-09-26 (nginx server_name
changed at 23:22) and api.math.tadrisino2.ir no longer resolves. The code
default for PUBLIC_BASE_URL and the docs' curl examples still named the dead
host, so every paymentUrl, the Zarinpal callback and the Bazaar redirect the
backend builds pointed nowhere. Historical status notes in CLAUDE.md keep the
old name on purpose. config/tests.py now reads the API host from
PUBLIC_BASE_URL instead of a literal. 624 tests green.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>