fix(mobile): update Node.js minimum requirement to 20.19.4

metro-config@0.83.3 uses Array.prototype.toReversed() which was added
in Node.js 20.0.0. The README incorrectly stated "Node.js 18+" causing
users to run `npx expo start` with Node 18 and hit:
  TypeError: configs.toReversed is not a function

- Update README.md to say "Node.js 20.19.4+" with nvm hint
- Update package.json engines from >=20.16.0 to >=20.19.4 to match
  metro-config's exact minimum (as declared in package-lock.json)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

mobile/README.md

@@ -14,7 +14,7 @@ Native mobile application for DocuElevate, built with **React Native** and **Exp
 
 ## Requirements
 
-- Node.js 18+
+- Node.js 20.19.4+ (use [nvm](https://github.com/nvm-sh/nvm): `nvm use` in this directory)
 - Expo CLI (`npm install -g @expo/cli`)
 - Expo Go app on device (for development) **or** Expo Application Services (EAS) for production builds
 - An Expo account: <https://expo.dev/>

mobile/package.json

@@ -55,7 +55,7 @@
     "typescript": "^5.3.0"
   },
   "engines": {
-    "node": ">=20.16.0"
+    "node": ">=20.19.4"
   },
   "private": true,
   "expo": {