fix: add GEMINI_API_KEY to docker-compose prod environment

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.prod.yml

@@ -31,6 +31,7 @@ services:
       SMTP_FROM: ${SMTP_FROM:-hello@letsbe.biz}
       ADMIN_EMAIL: ${ADMIN_EMAIL:-hello@letsbe.biz}
       OPENROUTER_API_KEY: ${OPENROUTER_API_KEY:-}
+      GEMINI_API_KEY: ${GEMINI_API_KEY:-}
     depends_on:
       db:
         condition: service_healthy