ci: bootstrap node before actions/checkout on Gitea runners

`actions/checkout@v4` is a JavaScript action — it expects `node` on
PATH in the runner image.  Gitea Actions (and local `act`) running
against `ubuntu:24.04` had neither node nor git pre-installed, so
checkout failed with:

  ❌  Failure - Main actions/checkout@v4
  exitcode '127': command not found

The pre-step now installs nodejs + git + ca-certificates from apt
before checkout runs.  The rest of the C++ toolchain installs in a
second step after the source tree is on disk.

Doesn't affect GitHub-hosted runners (their images already have node);
doesn't change build behaviour either.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -11,22 +11,32 @@ jobs:
     container:
       image: ubuntu:24.04
     steps:
-      - name: Install toolchain
+      # actions/checkout@v4 is a Node-based action; the bare ubuntu:24.04
+      # runner image has no node, so checkout fails with
+      # `exitcode '127': command not found`.  Install node + git BEFORE
+      # checkout, then install the rest of the toolchain after.
+      - name: Bootstrap (node + git for actions/checkout)
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
+          apt-get install -y --no-install-recommends \
+            git \
+            ca-certificates \
+            nodejs
+
+      - uses: actions/checkout@v4
+
+      - name: Install C++ toolchain
+        run: |
+          export DEBIAN_FRONTEND=noninteractive
           apt-get install -y --no-install-recommends \
             build-essential \
             cmake \
             ninja-build \
-            git \
             libasio-dev \
             libyaml-cpp-dev \
             python3 \
-            python3-yaml \
+            python3-yaml
-            ca-certificates
-
-      - uses: actions/checkout@v4
 
       - name: Configure
         run: cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release