fix(deps): force qs >= 6.15.2 to resolve DoS advisory

express 4 pins qs to ~6.14.0, which falls in the vulnerable range of
GHSA-q8mj-m7cp-5q26 (remotely triggerable TypeError in qs.stringify).
Add an npm override so the transitive dependency resolves to the patched
6.15.2.

package.json

@@ -21,6 +21,9 @@
   "devDependencies": {
     "nodemon": "^3.1.0"
   },
+  "overrides": {
+    "qs": "^6.15.2"
+  },
   "engines": {
     "node": ">=20"
   }