CI: install node+git in slim container so actions/checkout can run

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.forgejo/workflows/build.yml

@@ -17,6 +17,16 @@ jobs:
     container:
       image: python:3.12-slim
     steps:
+      # python:3.12-slim ships no node/git, but actions/checkout@v4 is a
+      # Node action — without this the job dies at checkout with
+      # `exec: "node": executable file not found`. Runs before checkout via
+      # the container shell (no node needed for a `run` step).
+      - name: Provide node + git for JS actions
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends git nodejs
+          rm -rf /var/lib/apt/lists/*
+
       - uses: actions/checkout@v4
 
       - name: Install deps