Add SMTP env vars to auth service in docker-compose (#5163)

The workflow writes SMTP credentials to .env, but docker-compose only
passes explicitly listed environment variables to containers.

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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.prod.yml

@@ -80,6 +80,11 @@ services:
       # JWT keys - PEM files in volume, bootstrapped from JWK on first run
       JWT_KEYS_PATH: "/etc/eagle0/keys"
       JWT_PRIVATE_KEY: "${JWT_PRIVATE_KEY:-}"
+      # SMTP credentials for sending invitation emails
+      SMTP_USERNAME: "${SMTP_USERNAME:-}"
+      SMTP_PASSWORD: "${SMTP_PASSWORD:-}"
+      SMTP_FROM_EMAIL: "${SMTP_FROM_EMAIL:-}"
+      SMTP_FROM_NAME: "${SMTP_FROM_NAME:-}"
     # Note: port 40033 is exposed via nginx, not directly
     volumes:
       - jwt-keys:/etc/eagle0/keys  # Shared JWT keys with Eagle