docs(changelog): add new entries from changelog

[windmill-internal-app]

This PR adds new changelog entries.

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Summary by cubic

Added a new changelog entry to the sidebar for "Fork data environments for DuckLake materialization" (2026-07-05), linking to the Windmill changelog. This makes the update visible in the Changelog navigation.

^{Written for commit 55ce840. Summary will update on new commits.}

[cloudflare-workers-and-pages]

Deploying windmill with    Cloudflare Pages

Latest commit:	55ce840
Status:	✅  Deploy successful!
Preview URL:	https://6349a7b1.windmill.pages.dev
Branch Preview URL:	https://changelog-update-28736517997.windmill.pages.dev

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[github-actions]

Pi Review

Good to merge.

This PR adds a single changelog entry to frontend/src/lib/components/sidebar/changelogs.ts — no code logic, no new APIs, no components changed.

Test coverage: This is a docs/config-only change (changelog data entries). No automated tests expected. No manual verification needed — the entry follows the established format and is purely a data addition.

[github-actions]

Codex Review

cc @windmill-internal-app[bot]
Mergeable, but should ideally address nits: broken changelog link

Found 1 issue:

1. [P2] Broken changelog link
   frontend/src/lib/components/sidebar/changelogs.ts:10

   The newly added sidebar changelog URL currently returns 404 from https://www.windmill.dev/changelog/fork-ducklake-data-environments, so users clicking the latest changelog entry will land on a not-found page. Please either deploy/add the matching changelog page or update the slug before merge.

Test coverage

Frontend-only static changelog data change; no automated tests are expected for this kind of entry.

Manual verification needed: open the Windmill sidebar changelog menu, click “Fork data environments for DuckLake materialization”, and confirm it opens the intended public changelog page instead of a 404.