refactor: separate thread from channel hoc

[isekovanic]

🎯 Goal

This PR separates the Thread HOC from the Channel one hierarchically. <Thread thread={thread}> now renders next to <Channel> instead of inside it. This removes the if (threadList) ... else ... branching across the SDK and stops opening a thread from running the channel's open sequence, which marked the channel read.

Stacked on perf/message-actions.

🛠 Implementation details

- <Channel channel={thread.channel} thread={thread} threadList>
-   <Thread />
- </Channel>
+ <Thread thread={thread}>
+   <MessageList />
+   <MessageComposer />
+ </Thread>

• <Channel> and <Thread> share a new internal ChannelShell (providers and config props), and each owns only its own lifecycle.
• Only <Thread> provides ThreadContext; useThreadContext() no longer throws and returns { thread: undefined } outside a thread.
• Rows in a thread read the thread's paginator. The last-bubble style comes from the row's neighbours instead of a paginator read.

Breaking changes

• <Channel> loses thread and threadList.
• <Thread> renders children, thread is required, and the old list/composer props are removed (parentMessagePreventPress moves to ThreadFooterComponent).
• The ThreadMessageComposer slot is removed.
• threadList is removed everywhere. Use useThreadContext().thread.
• ThreadContextValue is { thread?, allowThreadMessagesInChannel }, and onAlsoSentToChannelHeaderPress moved to MessagesContext.

Fixes

• Opening a thread, or pressing scroll-to-bottom in one, no longer marks the channel read.
• The unread separator and last-bubble style in a thread use the thread's own state.

🎨 UI Changes

/

🧪 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	2036 KB	2019 KB	-17229 B	🚀
ai_components_size	130 KB	130 KB	0 B	🟢