fix: remove rollup demo build from prepare script

The build:rollup step produces dist/ which is not included in the
package files field and is only used for the demo. Its dependency on
systemjs breaks on Node 20+ due to exports field enforcement.
Only run build:analyze:json in prepare, which is what consumers need.

Author: peschee

package.json

@@ -26,7 +26,7 @@
     "analytics"
   ],
   "scripts": {
-    "prepare": "npm run build",
+    "prepare": "npm run build:analyze:json",
     "build": "run-s build:**",
     "start": "es-dev-server --app-index demo/index.html --node-resolve --open --watch",
     "start:build": "npm run build && es-dev-server --root-dir dist --app-index index.html --compatibility none --open",