The base production.py hardcoded SAREX_API = https://srx.wb.ru, ignoring the
env, so issue export (GET /api/core/users/<id>/) failed from closed contours
with CERTIFICATE_VERIFY_FAILED. Read it from SAREX_API with the old value as
default; wb keeps it.
uralkal, vad, d8-ugmk-prod: SAREX_API -> backend-svc.django:80 (server-side
calls, no TLS), and SAREX_HOST set to the contour's public host so links in
exports and notifications stay external.
