fix(a11y): focus inputs on enter and page transitions

[isekovanic]

🎯 Goal

When a screen-reader user opens a channel or thread, VoiceOver/TalkBack focus previously landed on an arbitrary stop (the back button, or a message mid-list). This moves the entry point to where the user acts — the message composer — while keeping the header/back reachable via standard OS gestures.

• Add useSetAccessibilityFocus() - a public, generic primitive that moves the screen reader cursor onto a ref/node (SR-gated, RAF deferred). It only moves accessibility focus; it never opens the keyboard or activates the field.
• Add useScreenReaderMountFocus(ref) - built on the primitive; focuses on mount (and once the SR state resolves). MessageComposer uses it on inputBoxRef, so the composer is focused on entry. This is the path that lands Android forward navigation as well (but not always on iOS, which is why we need the actual transitional effect as well)

SampleApp reference implementation:

• useScreenReaderComposerFocusEffect - wires React Navigation's transitionEnd to useSetAccessibilityFocus, covering back navigation (both platforms) and iOS forward navigation (where firing on mount loses a race with the OS focus pass). Returns a stable setInputRef for <Channel>.
• Header reachability is done by adding accessibilityRole='header' on the screen header title (reachable via iOS Headings rotor / jump to top and Android Headings reading control swipe up) and onAccessibilityEscape -> goBack on the screen root for the iOS back scrub (Android uses the system Back gesture).

Note: onAccessibilityEscape is inert on a layout only View under Fabric - it gets flattened and never receives the gesture. The view hosting it needs collapsable={false} if it does not apply any layout relevant props itself.

🛠 Implementation details

🎨 UI Changes

iOS

Before	After

Android

Before	After

🧪 Testing

☑️ Checklist

• I have signed the Stream CLA (required)
• PR targets the develop branch
• Documentation is updated
• New code is tested in main example apps, including all possible scenarios
  • SampleApp iOS and Android
  • Expo iOS and Android

[Stream-SDK-Bot]

SDK Size

title	develop	branch	diff	status
js_bundle_size	1955 KB	1957 KB	+2080 B	🔴