chore: declare node >=20, the version the box actually runs

Was: >=18.

Eighteen of thirty repos declared no Node version at all, and the twelve
that did used five spellings of the same intent - >=18, >=20, >=20.0.0,
>=22, >=22.19.0. The box runs 20.20.2, so >=22 was a claim nothing could
satisfy and nothing would have caught.

One spelling, matching the machine that runs it, turns an invisible
mismatch into a loud one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UvjGNAS9CMfEGNW26tUR4P

Author: catomean

package.json

@@ -24,7 +24,7 @@
   "type": "module",
   "sideEffects": false,
   "engines": {
-    "node": ">=18"
+    "node": ">=20"
   },
   "publishConfig": {
     "access": "public",