Realize scheduled releases for solution-arsenal and artifact-conduit #43

Releases only happen when someone remembers to start one. The shared release workflow should cut a draft release on a schedule from the newest commit on main where all required checks passed, and open an issue so the release owner reviews and publishes it. Publishing stays manual.

Depends on: #42

AC

• The shared release workflow runs on a schedule (cadence set per repo) and cuts a draft release from the newest commit on main whose required checks all passed.
• If nothing releasable has landed, the run is skipped; if there's no green commit or the previous draft is still pending, the run fails.
• A new draft or a failed run opens an issue assigned to the release owner; the issue closes when the release is published or the draft is discarded.
• Cadence, release owner and cutoff are documented in dev-kit.

Out of scope: publishing automatically and major versions (these stay manual).