chore: gate TypeScript duplication in CI

package.json

@@ -17,6 +17,7 @@
     "typecheck": "tsc -b tsconfig.json",
     "lint": "eslint .",
     "lint:fix": "eslint . --fix",
+    "duplication": "jscpd --config .jscpd.json packages",
     "test": "vitest run",
     "test:coverage": "vitest run --coverage",
     "test:e2e": "vitest run --config vitest.e2e.config.ts",
@@ -81,7 +82,9 @@
     "@types/node": "^22.20.0",
     "@vitest/coverage-v8": "^4.1.8",
     "eslint": "^10.4.1",
+    "eslint-plugin-sonarjs": "^4.1.0",
     "fast-check": "^4.8.0",
+    "jscpd": "^5.0.12",
     "jsdom": "29.1.1",
     "knip": "^6.16.1",
     "lefthook": "^2.1.9",