Raise minimum Node.js version to 22.18.0 (#37058)

Remove the experimental strip types check and `NODE_VARS` mechanism from
the Makefile, as Node.js 22.18.0+ has native TypeScript type stripping
support.

https://nodejs.org/en/blog/release/v22.18.0 was released 8 months ago
and has now trickled into all major Linux distros like Alpine 3.23+.

---
This PR was written with the help of Claude Opus 4.6

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>

package.json

@@ -2,7 +2,7 @@
   "type": "module",
   "packageManager": "pnpm@10.33.0",
   "engines": {
-    "node": ">= 22.6.0",
+    "node": ">= 22.18.0",
     "pnpm": ">= 10.0.0"
   },
   "dependencies": {