fix(auth): add undici instrumentation for Squid proxy

Without it, NextAuth's Keycloak issuer-discovery fetch goes direct
and Calico default-deny drops it → /access-denied?error=Configuration.
EnvHttpProxyAgent reads HTTP(S)_PROXY at startup.

Mirrors gscAdmin/src/instrumentation.ts. + undici ^6.25.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -25,6 +25,7 @@
     "pg": "^8.20.0",
     "react": "^19.2.3",
     "react-dom": "^19.2.3",
+    "undici": "^6.25.0",
     "zod": "^3.23.0"
   },
   "devDependencies": {