[prathshenoy]

Summary

What:

• Add queue-scoped storage for open-issue references with bounded listing and conditional replacement or deletion.

Why:

• Avoid scanning retained closed summaries to find open issues. Summaries intentionally keep closed records for ordering, so a separate lookup provides the access path for the upcoming open-issues view. Populating that lookup and exposing it through an API remain follow-up work.
• Protect a newer opening from an old close. The same issue key can close and reopen, so replacement and deletion must check which opening they are changing. Reuse the existing table without adding columns or changing operational issue tracking.

Test Plan

• Add unit tests.
• Verify conditional writes and bounded listing against a real MySQL database.

Revert Plan

• Revert this PR. No runtime writer uses the lookup, and the existing table layout is unchanged.

Issue Links

• CODEM-607

Stack

1. feat(stovepipe): Add issue summary storage #982
2. feat(stovepipe): Materialize issue summaries #983
3. feat(stovepipe): Add open issue lookup storage #984
4. feat(stovepipe): Maintain open issue lookups #986
5. feat(stovepipe): Add open issue listing #988
6. feat(stovepipe): Expose open issue listing #990
7. feat(stovepipe-web): Show open issues #993