Docs CI: re-emit sphinx warnings as GitHub annotations on failure

Previous attempt uploaded the log as an artifact but the public
artifacts API returns 0 artifacts for failed runs without auth.
Add a failure-only step that cats the log to stdout and re-emits
matching WARNING/ERROR lines as ::error:: annotations, which ARE
exposed via the public check-run annotations API.

Author: ncbdrck

.github/workflows/docs.yml

@@ -73,16 +73,31 @@ jobs:
       - name: Build HTML docs (warnings-as-errors)
         working-directory: UniROS
         run: |
+          mkdir -p docs/_build
           set -o pipefail
           sphinx-build -W --keep-going -b html docs docs/_build/html 2>&1 | tee docs/_build/sphinx.log
 
+      - name: Surface sphinx warnings as annotations
+        if: failure()
+        working-directory: UniROS
+        run: |
+          echo "===== sphinx.log ====="
+          cat docs/_build/sphinx.log || echo "(no log file)"
+          echo "===== warning lines ====="
+          grep -nE "(WARNING|ERROR)" docs/_build/sphinx.log || echo "(no warnings matched)"
+          # Re-emit as GitHub annotations so they surface via the check-run API.
+          while IFS= read -r line; do
+            echo "::error::${line}"
+          done < <(grep -E "(WARNING|ERROR)" docs/_build/sphinx.log || true)
+
       - name: Upload sphinx build log
         if: always()
         uses: actions/upload-artifact@v4
         with:
           name: sphinx-log
           path: UniROS/docs/_build/sphinx.log
           retention-days: 14
+          if-no-files-found: warn
 
       - name: Upload built docs as artifact
         if: success()