Add event-driven prerelease retention cleanup

[anand-testcompare]

We should add an event-driven cleanup step for GitHub prereleases so release asset storage does not grow indefinitely.

Current inventory found about 17 non-draft prereleases in this repo. Tag/release shape: v<version>-rc.<n>.

Reference implementation: shpitdev/meshix-mono#42

Acceptance criteria:

• Cleanup is triggered by release/prerelease workflows, not a cron-only job.
• Stable releases are kept for now; do not archive/delete stable releases in this task.
• Rolling prereleases keep only one active release family, e.g. keep v0.0.17-next.* while deleting older v0.0.16-next.* families.
• When a stable release is published, prereleases that fed that stable line are removed with their tags.
• Run/document a dry-run before enabling destructive deletion.
• If this repo has multiple release tracks, scope cleanup by tag prefix so one track does not delete another track's prereleases.