fix: allow staging reusable workflow checkout (#566)

Grant the reusable ingest job contents read permission so the called workflow can check out the app repository without exceeding the caller permission ceiling.

中文：允许预发布可复用工作流检出代码。为可复用写入任务授予 contents 读取权限，使被调用工作流能够检出应用仓库，同时不超出调用方的权限上限。

Author: cquil11

.github/workflows/stage-results.yml

@@ -196,6 +196,8 @@ jobs:
   ingest:
     name: Ingest selected run
     needs: [validate, refresh-staging-database]
+    permissions:
+      contents: read
     uses: ./.github/workflows/ingest-agentic-results.yml
     with:
       run-id: ${{ needs.validate.outputs.run-id }}