fix(packaging): sign native Node.js addons for Apple notarization (#78) Pi SDK's transitive npm dependencies include prebuilt native addons (*.node files, e.g. @mariozechner/clipboard-darwin-universal). Apple notarization requires every Mach-O binary in the bundle to be signed. Add a step in sign_sidecar_node_binaries() to find and sign all .node files under pi-sidecar/node_modules/.