Add pnpm override to force dompurify >=3.4.0 across playground deps

A playground file-dep (antenna-component-library) was still pulling
dompurify@3.3.3 transitively, leaving it in the root lockfile and keeping
Dependabot alert #9 open. Override in package.json pins everything to
>=3.4.0, so the lockfile now only resolves 3.4.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kurtstohrer

package.json

@@ -53,7 +53,8 @@
     "overrides": {
       "follow-redirects": ">=1.16.0",
       "defu": ">=6.1.5",
-      "lodash": ">=4.18.0"
+      "lodash": ">=4.18.0",
+      "dompurify": ">=3.4.0"
     }
   },
   "engines": {