[core][xs]: specify folder to publish

.changeset/tasty-impalas-hug.md

@@ -0,0 +1,5 @@
+---
+'@portaljs/core': patch
+---
+
+Fix what's getting published to npm by specifying `files` in package.json.

packages/core/package.json

@@ -16,6 +16,7 @@
   "publishConfig": {
     "access": "public"
   },
+  "files": ["dist"],
   "type": "module",
   "main": "./dist/index.js",
   "dependencies": {