fix(ci): restore broken YAML structure in 3 workflows, revert aggressive STALE_HOURS

- pr-auto-response.yml: restore permissions, steps, and checkout in
  contributor-tier-issues job (broken by runner swap)
- pr-check-stale.yml: restore steps block and step name
- pr-intake-checks.yml: restore steps block, checkout, and timeout
- pr-check-status.yml: revert STALE_HOURS from 4 to 48 (not a cost
  optimization; 4h is too aggressive), switch to ubuntu-latest per
  PR description

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/pr-check-stale.yml

@@ -13,6 +13,8 @@ jobs:
             issues: write
             pull-requests: write
         runs-on: ubuntu-latest
+        steps:
+            - name: Mark stale issues and pull requests
               uses: actions/stale@b5d41d4e1d5dceea10e7104786b73624c18a190f # v10.2.0
               with:
                   repo-token: ${{ secrets.GITHUB_TOKEN }}