Update dependency purgecss to v6

ui/package.json

@@ -8,7 +8,7 @@
     "base64-js": "1.5.1",
     "bootstrap": "5.3.3",
     "esbuild": "0.19.3",
-    "purgecss": "5.0.0",
+    "purgecss": "6.0.0",
     "sass": "1.77.6"
   }
 }