chore: pin publishConfig to public npm registry

Force publishes to registry.npmjs.org with public access so an ambient
@forkzero -> npm.pkg.github.com scope mapping can't redirect npm publish to
GitHub Packages (the E403 seen on the first manual publish attempt).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: gmoon

package.json

@@ -5,6 +5,10 @@
   "type": "module",
   "license": "Apache-2.0",
   "author": "George Moon <george.moon@gmail.com>",
+  "publishConfig": {
+    "access": "public",
+    "registry": "https://registry.npmjs.org"
+  },
   "repository": {
     "type": "git",
     "url": "git+https://github.com/forkzero/s3-website-test-kit.git"