Adds new Authentik (v2025.10.0) authentication/SSO stack with: - Redis cache service - Authentik server (exposed at auth.frostlabs.me via Traefik) - Authentik worker for background tasks - Fixed depends_on references to use correct service name (redis) - External PostgreSQL backend at 10.0.4.10 - Docker secrets integration for sensitive credentials 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>