chore: Remediate 3 Dependabot security alerts (react-router-dom 6→7) (#169)

Upgrade react-router-dom from ^6.30.4 to ^7.18.2 to resolve:
- GHSA-wrjc-x8rr-h8h6 (react-router open redirect, CVE-2026-53669)
- GHSA-337j-9hxr-rhxg (react-router constructor injection, CVE-2026-53666)
- GHSA-jjmj-jmhj-qwj2 (react-router-dom, CVE-2026-53668)

All affected packages are dev-only dependencies.

Author: ernst-dev

package-lock.json

@@ -119,7 +119,7 @@
     "puppeteer-core": "^22.15.0",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
-    "react-router-dom": "^6.30.4",
+    "react-router-dom": "^7.18.2",
     "size-limit": "^11.1.2",
     "stylelint": "^16.8.1",
     "stylelint-config-recommended-scss": "^14.1.0",