docs(changelog): add new entries from changelog

[windmill-internal-app]

This PR adds new changelog entries.

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Summary by cubic

Adds a new changelog item to the sidebar for "Schema contracts for pipeline consumers," linking to the published entry and dated 2026-07-05. This makes the latest changelog visible in the app’s list.

^{Written for commit 85df0e6. Summary will update on new commits.}

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Latest commit:	85df0e6
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Branch Preview URL:	https://changelog-update-28736270363.windmill.pages.dev

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[github-actions]

Pi Review

Good to merge.

This is a straightforward changelog entry addition. The new entry follows the existing format and is correctly placed at the top of the reverse-chronological list. No code changes, no new public surfaces, no security concerns.

Test coverage: This is a docs-only change (static data in a frontend TypeScript file). No automated tests expected. No manual verification needed beyond confirming the changelog page at https://www.windmill.dev/changelog/pipeline-schema-contracts exists and loads correctly.

[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 new sidebar entry points to https://www.windmill.dev/changelog/pipeline-schema-contracts, which currently resolves to Windmill’s 404 page. Since SidebarContent.svelte renders these changelog entries as external Help menu links, merging this adds a visible broken link for users. Please publish the target page first or update href to the actual slug.

Test Coverage

Frontend static data only; no automated tests are expected for this change.

Manual verification still needed: open the app sidebar Help menu, click “Schema contracts for pipeline consumers,” and confirm it opens the intended changelog page rather than a 404.