[Customer account UI extensions 2026-04-rc]: Improved descriptions for "Layout and structure" components

[mcvinci]

This PR:

• Improves JSDoc descriptions for layout and structure components for checkout / customer accounts to align with admin UI extensions documentation style — clearer opening sentences, bulleted value descriptions for enum props (background, borderRadius, accessibilityRole, alignContent, etc.), and inline "Learn more about" links replacing @see tags.
• Adds missing descriptions for BorderShorthand, SpacingKeyword, OverflowKeyword, ReducedAlignContentKeyword, ReducedAlignItemsKeyword, ReducedJustifyContentKeyword, ReducedJustifyItemsKeyword, and the AccessibilityRole union type, ensuring all public types are documented.
• Updated components-shared.d.ts and components.d.ts to keep upstream descriptions consistent with the component-level overrides, removing internal @implementation annotations, @see tags, and vague phrasing like "Adjust spacing between elements" or "Sets the semantic meaning."
• Adds full property-level descriptions for Docs_Page_Button_PrimaryAction, Docs_Page_Button_SecondaryAction, and Docs_Page_Button_BreadcrumbAction in the customer account API docs, and updates Page slot descriptions with documentation links and improved wording.
• Removes duplicate descriptions from customer account components.d.ts doc type aliases (PagePropsDocs, SectionPropsDocs, PageElementSlotsDocs, SectionElementSlotsDocs) that were being pulled into generated docs alongside the source definitions.
• Relates to https://github.com/shop/world/pull/579467
• Partially closes https://github.com/shop/issues-learn/issues/1008

[github-actions]

🚨🚨🚨 Docs migration in progress 🚨🚨🚨

We are actively migrating UI extension reference docs to MDX in the areas/platforms/shopify-dev zone of the monorepo. This impacts docs for the following surfaces:

• Admin UI extensions
• App Home
• Checkout UI extensions
• Customer account UI extensions
• POS UI extensions

During this migration, please be aware of the following:

.doc.ts files are being deprecated. Changes to .doc.ts files in this repo will not be reflected in the new MDX-based docs. If you need to update docs for a reference that has already been migrated, make your changes directly in the areas/platforms/shopify-dev zone of the monorepo instead.

Doc comments in .ts source files (the comment blocks above types and functions) are also affected. Generating docs from these comments currently requires a newer version of the @shopify/generate-docs library that isn't yet available. Updates to doc comments may not produce the expected output until the migration is complete.

Examples that previously lived in this repo are being moved to the areas/platforms/shopify-dev zone of the monorepo and should be authored there going forward.

What should I do?

• If your PR includes changes to .doc.ts files, doc comments, or examples, please reach out to us in #devtools-proj-templated-refs so we can help ensure your updates are captured correctly.
• If your PR is limited to source code changes (non-docs), you can ignore this notice.

Thanks for your patience while we complete the migration! 🙏