chore(DialogV1): remove sx from deprecated Dialog

[francinelucca]

Closes#6776

Current sx usage: 0

Changelog

Removed

Remove support for sx from the DialogV1 deprecated component, and associated stories, docs, and tests

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 848563c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[Copilot]

Pull Request Overview

This PR removes the sx prop support from the deprecated DialogV1 component as part of the migration away from styled-components. The change is part of a broader effort to eliminate sx prop usage across deprecated components.

• Removes SxProp and sx prop support from DialogV1 component and its Header subcomponent
• Replaces BoxWithFallback wrapper components with native HTML elements
• Updates styled-react package to provide its own DialogV1 wrapper that maintains sx support for backward compatibility

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/react/src/DialogV1/Dialog.tsx	Removes sx prop support and BoxWithFallback wrapper, adds as prop for component polymorphism
packages/styled-react/src/components/DialogV1.tsx	New wrapper component that adds back sx prop support using Box component
packages/styled-react/src/deprecated.tsx	Updates Dialog export to use local DialogV1 wrapper instead of direct import
packages/styled-react/src/tests/primer-react-deprecated.browser.test.tsx	Updates tests to verify sx prop functionality with new wrapper
.changeset/modern-chicken-happen.md	Documents breaking change for major version bump

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/3554

[primer-integration]

🟢 ci completed with status success.

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!