- Move Vikunja DB user/password/database and JWT secret to environment variables
- Update .env.example with clear sections and 'change-me' placeholders
- Update SECURITY.md to reflect that more secrets now live in .env
- docker-compose.yml: read authkey and login server from env
- README.md: updated instructions to use env vars instead of editing the file
- Added .gitignore for secrets and Tailscale state