Clearview stack: drop ONBOARDING_* passthrough from compose

Config belongs in the database (fixed convention); the stack carries only what
the app needs to start. Onboarding is no longer wired through the compose.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

stack/docker-compose.yml

@@ -8,9 +8,6 @@ services:
     environment:
       TZ: ${TZ:?set TZ}
       DATABASE_URL: postgresql://${POSTGRES_USER:?set POSTGRES_USER}:${POSTGRES_PASSWORD:?set POSTGRES_PASSWORD}@${POSTGRES_HOST:?set POSTGRES_HOST}:${POSTGRES_PORT:?set POSTGRES_PORT}/${POSTGRES_DB:?set POSTGRES_DB}
-      ONBOARDING_CLIENT_ID: ${ONBOARDING_CLIENT_ID:-}
-      ONBOARDING_CLIENT_SECRET: ${ONBOARDING_CLIENT_SECRET:-}
-      ONBOARDING_REDIRECT_URI: ${ONBOARDING_REDIRECT_URI:-}
     depends_on:
       postgres:
         condition: service_healthy