Externalise use-sync-external-store in petrinaut lib build

@tanstack/react-form → @tanstack/react-store pulls in the pure-CJS
use-sync-external-store, whose `require("react")` calls were surviving
rolldown's lib build (react is external) as a runtime require helper
that throws in the browser. Externalising use-sync-external-store and
its subpaths pushes the CJS→ESM interop to the consumer's bundler,
which handles it via pre-bundling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kube

libs/@hashintel/petrinaut/vite.config.ts

@@ -22,6 +22,12 @@ export default defineConfig(({ command }) => ({
         "react-dom",
         "@xyflow/react",
         "@babel/standalone",
+        // Pure-CJS dep pulled in transitively by @tanstack/react-form →
+        // @tanstack/react-store. Rolldown can't safely transform its
+        // `require("react")` when react is external, so it falls back to a
+        // runtime require helper that throws in the browser. Externalising it
+        // pushes CJS→ESM interop to the consumer's bundler.
+        /^use-sync-external-store(\/.*)?$/,
       ],
       output: {
         globals: {