ci: bump Node to 20.19.0 — vitest 4 / rolldown needs util.styleText

`npm test` (vitest 4.1.6 -> rolldown 1.0.1) imports `styleText` from
`node:util`, which only exists from Node 20.12.0. CI, .nvmrc, and the
engines floor were pinned to 20.9.0, so `vitest run` crashed at startup
with "does not provide an export named 'styleText'". Raise CI + .nvmrc to
20.19.0 (latest 20.x LTS) and the engines floor to >=20.12.0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: holkexyz

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '20.9.0'
+          node-version: '20.19.0'
           cache: npm
 
       - name: Install dependencies

.nvmrc

@@ -1 +1 @@
-20.9.0
+20.19.0

package.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "engines": {
-    "node": ">=20.9.0"
+    "node": ">=20.12.0"
   },
   "scripts": {
     "dev": "next dev",