fix: harden partial 429 success, fallbacks, zh errors

Retry HTTP 429 with backoff; keep models beyond first 3 as
fallbacks; degrade agreement when some models fail; force-high
risk only if zero usable responses. Clearer zh-CN errors/docs for
dogfood uses: ./ rebase + workflow_dispatch re-run.

action.yml

@@ -58,10 +58,18 @@ runs:
     # Runner image / consumer workflow must provide Node >= 18.
     - name: Require Node.js
       shell: bash
+      env:
+        GATEKEEP_LANGUAGE: ${{ inputs.language }}
       run: |
         if ! command -v node >/dev/null 2>&1; then
-          echo "::error::Node.js >= 18 required for Gatekeep (merge-findings.js / publish.js)."
-          echo "Preinstall Node on the runner, or add a mirrored setup-node step before uses: ./."
+          lang="${GATEKEEP_LANGUAGE:-}"
+          if [[ "${lang,,}" == zh* ]]; then
+            echo "::error::Gatekeep 需要 Node.js ≥ 18（merge-findings.js / publish.js）。"
+            echo "请在 runner 预装 Node，或在 uses: ./ 之前加本 forge 已镜像的 setup-node；不要依赖未镜像的 actions/setup-node。"
+          else
+            echo "::error::Node.js >= 18 required for Gatekeep (merge-findings.js / publish.js)."
+            echo "Preinstall Node on the runner, or add a mirrored setup-node step before uses: ./."
+          fi
           exit 1
         fi
         node --version