Add quiz-lead internal endpoint for Typebot → Listmonk funnel

POST /api/internal/quiz-lead accepts archetype quiz results and
idempotently upserts subscriber in Listmonk (create on 201, PUT on 409).
Documents QUIZ_LEAD_SECRET and LISTMONK_* vars in .env.example.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -24,3 +24,11 @@ INTERNAL_GRANT_SECRET=""
 
 # Freemium: slug бесплатного курса, в который авто-записываем новых юзеров при регистрации
 FREE_COURSE_SLUG=obsidian-start
+
+# Freemium quiz funnel (Typebot → /api/internal/quiz-lead)
+QUIZ_LEAD_SECRET=""
+# Listmonk API base — публичный домен (Listmonk живёт на Hetzner, наружу через newsletter.)
+LISTMONK_URL="https://newsletter.second-brain.ru"
+LISTMONK_USER="apiuser"
+LISTMONK_TOKEN=""
+LISTMONK_QUIZ_LIST_ID=""