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-auto-response.yml

@@ -16,6 +16,15 @@ jobs:
       (github.event_name == 'pull_request_target' &&
       (github.event.action == 'labeled' || github.event.action == 'unlabeled'))
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      issues: write
+      pull-requests: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Apply contributor tier label for issue author
         uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8
         env:
           LABEL_POLICY_PATH: .github/label-policy.json