chore: add Node version management and update engine requirements

Add .nvmrc file specifying Node 20.18.1 LTS for consistent development
environment. Update package.json engines to require Node 20-22 to align
with security resolution requirements and ensure compatibility.

Author: MSACC

.nvmrc

@@ -0,0 +1 @@
+20.18.1

package.json

@@ -134,7 +134,7 @@
   },
   "homepage": "https://www.pluginpal.io/plugin/config-sync",
   "engines": {
-    "node": ">=18.0.0",
+    "node": ">=20.0.0 <=22.x.x",
     "npm": ">=6.0.0"
   },
   "license": "MIT",