ci: raise duplication threshold to 4 percent

Set the repository jscpd ceiling to the requested 4%. Preserve the scan
inventory, token/line minima, ignore rules and report failure propagation.

Validation: npm run jscpd passed at 3.59% duplication; scoped format check passed.

.jscpd.json

@@ -1,5 +1,5 @@
 {
-  "threshold": 3.5,
+  "threshold": 4,
   "reporters": ["consoleFull"],
   "ignore": [
     "node_modules/**",