Fix: Let's Encrypt status detection and auto-generate .env

- AdminController: Detect existing SSL certificates from /etc/letsencrypt
  and update database status automatically (fixes status showing "none"
  when cert was obtained via cloud-init)
- docker-compose.prod.yml: Mount /etc/letsencrypt to backend container
- cloud-init: Auto-generate .env with secure random secrets on first boot
  (DB_PASSWORD, JWT_SECRET, REDIS_PASSWORD, OME_API_TOKEN, NAKAMA keys)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.prod.yml

@@ -81,6 +81,7 @@ services:
     volumes:
       - ./config.json:/app/config.json
       - uploads:/app/uploads
+      - /etc/letsencrypt:/etc/letsencrypt:ro
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:8080/api/health"]
       interval: 10s