ci: update README and CI workflow to improve bird2 job installation process and clarify Docker usage

.gitea/workflows/ci.yaml

@@ -86,12 +86,20 @@ jobs:
     needs: [go]
     steps:
       - uses: actions/checkout@v4
+      # Вложенный docker + bind-mount ломается, если демон Docker на хосте не видит путь
+      # workspace runner'а (/workspace/...). bird -p на самом job-раннере надёжнее.
+      - name: Install bird2
+        run: |
+          set -euxo pipefail
+          if command -v sudo >/dev/null 2>&1; then SUDO=sudo; else SUDO=""; fi
+          $SUDO apt-get update -qq
+          DEBIAN_FRONTEND=noninteractive $SUDO apt-get install -y -qq bird2
+          bird --version
       - name: bird -p on all scenario bird.conf files
         env:
           WORKSPACE: ${{ github.workspace }}
         run: |
           set -euxo pipefail
-          # $PWD на act/Gitea runner не всегда корень репозитория; монтируем именно checkout.
           WS="${WORKSPACE:-$PWD}"
           cd "$WS"
           if [ ! -f internal/birdfmt/testdata/scenarios/minimal/bird.conf ]; then
@@ -101,9 +109,5 @@ jobs:
           fi
           for conf in internal/birdfmt/testdata/scenarios/*/bird.conf; do
             echo "==> $conf"
-            docker run --rm \
-              -e "BIRD_CONF=/work/${conf}" \
-              -v "${WS}:/work:ro" \
-              debian:bookworm-slim \
-              bash -ceu 'apt-get update -qq && DEBIAN_FRONTEND=noninteractive apt-get install -y -qq bird2 >/dev/null && bird -c "$BIRD_CONF" -p'
+            bird -c "$WS/$conf" -p
           done