Install Node in the CI job container before checkout

actions/checkout is a JS action and needs a node binary on PATH; the
php:8.3-cli-alpine job container doesn't ship one, so checkout was
failing with "node: executable file not found in $PATH".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -9,6 +9,12 @@ jobs:
     runs-on: ubuntu-latest
     container: php:8.3-cli-alpine
     steps:
+      # actions/checkout is a JS action -- php:8.3-cli-alpine has no node on
+      # PATH by default, so install it (musl-native, no glibc/Alpine mismatch)
+      # before any step that needs it.
+      - name: Install Node
+        run: apk add --no-cache nodejs
+
       - uses: actions/checkout@v4
 
       - name: Install Composer