ci: update Node.js test matrix to 20, 22, 24

- Remove Node 18 (EOL April 2024)
- Add Node 24 (latest release April 2025)
- Keep Node 20 and 22 (current LTS versions)

Author: claude

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: ['18', '20', '22']
+        node-version: ['20', '22', '24']
       fail-fast: false
 
     steps: