- Add config validation: signing_key required, minimum 32 characters
- Server now fails to start without valid signing_key (no more runtime errors)
- Add config.example.yml with default whitelist hosts
- Copy config to /etc/pixa/config.yml in Docker image
- Update entrypoint to use --config /etc/pixa/config.yml
- Add config.dev.yml for local Docker development
- Mount dev config in make devserver
