chore: S2 docs followup

[reidbarber]

Minor cleanup for the s2 docs:

• make 'ArrowDown' open the SearchMenu onKeyDown
• fix chevron in SearchMenu's trigger action button
• fix Github logo
• header/menu layout improvements

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs

[rspbot]

## API Changes

react-aria-components

/react-aria-components:useContextProps

 useContextProps <E extends Element, T, U extends SlotProps> {
   props: (T & SlotProps)
-  ref: ForwardedRef<E> | undefined
+  ref: ForwardedRef<E>
   context: Context<ContextValue<U, E>>
   returnVal: undefined
 }

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