SelectPanel: Add new prop align to SelectPanel

[TylerJDev]

Closes https://github.com/github/primer/issues/5294

Adds prop align to SelectPanel to allow consumers to adjust where the SelectPanel will be upon opening.

Changelog

New

• Adds new prop align to SelectPanel

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)

[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 introduces a new align prop for SelectPanel to control its horizontal position relative to the anchor element.

• Adds align to the SelectPanelBaseProps interface and forwards it to AnchoredOverlay.
• Updates the documentation JSON to include the new align prop.
• Adds a changeset for a minor release.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/react/src/SelectPanel/SelectPanel.tsx	Added optional align prop and passed it into AnchoredOverlay.
packages/react/src/SelectPanel/SelectPanel.docs.json	Documented the new align prop with its type, default, and description.
.changeset/fluffy-baboons-sip.md	Added a changeset entry marking this as a minor release.

Comments suppressed due to low confidence (3)

packages/react/src/SelectPanel/SelectPanel.tsx:186

• [nitpick] To make the default alignment explicit in the component API, consider assigning a default value (e.g., align = 'start') when destructuring the props.

align,

packages/react/src/SelectPanel/SelectPanel.tsx:632

• There are no tests covering the new align prop. Consider adding unit or integration tests to verify the panel’s positioning for different align values.

align={align}

packages/react/src/SelectPanel/SelectPanel.docs.json:196

• [nitpick] The defaultValue entry includes single quotes inside the JSON string, which may render extra quotes in the generated docs. Consider using "defaultValue": "start" for clarity.

"defaultValue": "'start'",

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	94.59 KB (+0.09% 🔺)
packages/react/dist/browser.umd.js	94.68 KB (+0.05% 🔺)

[francinelucca]

✨

[francinelucca]

nit: could add to Pick<> in line 119 instead

[TylerJDev]

Oh wow, didn't even realize! thank you for the suggestion! 🙏

[changeset-bot]

🦋 Changeset detected

Latest commit: 354d5e7

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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