AtAuth

docs: fix Quick Start, docker-compose env passthrough, HOMELAB master

- docker-compose.yml: use env_file instead of individual env vars, fixing missing OIDC/passkey/MFA config that broke Docker deployments - README: add prerequisites, verify step, app configuration step, CORS_ORIGINS to domain config, forward-auth env var instructions, passkey feature mention - HOMELAB: update deploy section to match README flow, add all 20 presets, add forward-auth env setup, add CORS troubleshooting - .env.example: note Docker Compose DB_PATH override