Wire BROUTER_URL into the journal service

The demo-bot calls BRouter to generate GPX for Bruno's walks, and the
route-compute API does the same on the journal side. Neither had
BROUTER_URL set on prod, so both fell back to http://localhost:17777
inside the journal container and every request returned upstream-error.
Point the journal at the brouter service on the internal docker
network the same way the planner does.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

infrastructure/docker-compose.yml

@@ -23,6 +23,7 @@ services:
       DOMAIN: ${DOMAIN:-trails.cool}
       ORIGIN: https://${DOMAIN:-trails.cool}
       PLANNER_URL: https://planner.${DOMAIN:-trails.cool}
+      BROUTER_URL: http://brouter:17777
       DATABASE_URL: postgres://trails:${POSTGRES_PASSWORD:-trails}@postgres:5432/trails
       JWT_SECRET: ${JWT_SECRET:-change-me-in-production}
       SESSION_SECRET: ${SESSION_SECRET:-change-me-in-production}