chore(staging): wire LEADERBOARD_INCLUDE_TEST_DEFAULT into compose

The v3.3.5 router reads config.LEADERBOARD_INCLUDE_TEST_DEFAULT but the
staging compose file was never passing the env through to the container.
This change was applied manually on the staging host before but never
made it back into the repo — fixing that so CI deploys pick it up.

Value on staging is sourced from .env (already set to true). Production
leaves it unset, so the default of false applies.

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

docker-compose.staging.yml

@@ -35,6 +35,7 @@ services:
       - BOOTSTRAP_ADMIN_USERNAME=${BOOTSTRAP_ADMIN_USERNAME:-}
       - BOOTSTRAP_ADMIN_PASSWORD=${BOOTSTRAP_ADMIN_PASSWORD:-}
       - MATCHMAKING_ENABLED=true
+      - LEADERBOARD_INCLUDE_TEST_DEFAULT=${LEADERBOARD_INCLUDE_TEST_DEFAULT:-false}
     depends_on:
       postgres:
         condition: service_healthy