fix: publish scoped npm launcher

[jmagar]

Summary

• publish the Node launcher as @dinglebear/rtailscale
• align MCP Registry identity to ai.dinglebear/rtailscale
• enforce public scoped-package metadata and token-backed release authentication
• preserve existing binary, archive, and package-directory contracts

Verification

• npm tests and package validation
• npm pack dry run and tarball install smoke
• actionlint and JSON/schema checks
• git diff --check