v26.13 release notes

[bosconi]

For included items with PR links see: https://github.com/MaterializeInc/docs-automation/blob/main/release-notes/output/release_notes_v26.13.md

For omitted items with PR links see: https://github.com/MaterializeInc/docs-automation/blob/main/release-notes/output/release_notes_v26.13_omitted.md

[github-actions]

Thanks for opening this PR! Here are a few tips to help make the review process smooth for everyone.

PR title guidelines

• Use imperative mood: "Fix X" not "Fixed X" or "Fixes X"
• Be specific: "Fix panic in catalog sync when controller restarts" not "Fix bug" or "Update catalog code"
• Prefix with area if helpful: compute: , storage: , adapter: , sql:

Pre-merge checklist

• The PR title is descriptive and will make sense in the git log.
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• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.
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[def-]

I think this is the least impressive improvement, should be at the end

[maheshwarip]

All improvements are special, but some improvements are more special than others

[maheshwarip]

@kay-kim ready for review!

[kay-kim]

would tick SUBSCRIBE and include a comma

`SUBSCRIBE`, and