feat: Implement forum topics support

[japananimetime]

Adds complete forum topics functionality:

• ForumTopicsController: Main topics list with search, create, edit, delete
• ForumTopicView: Custom view for topic items with icons/avatars
• ForumTopicTabsController: ViewPager tabs layout for topics
• Topic message filtering using GetForumTopicHistory
• Per-topic unread counters, mentions, and reactions
• Topic notification settings (mute/unmute)
• Topic typing indicators
• Topic header in chat view
• Navigation integration
• Forum toggle in group settings
• View as chat/topics toggle
• Notification separation showing "Chat > Topic"

🤖 Generated with Claude Code

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[LeeseTheFox]

I tested this and found a bug where topic names and message previews would sometimes show the wrong content, especially in big active chats. For a split second the correct names would show, then they change to different topics. Looks like it was a race condition with RecyclerView recycling.

Here's the fix for ForumTopicView.java:

1. In setTopic() method, right after clearing the receivers, add:

displayTitle = null;
displaySender = null;
displayPreview = null;

2. In buildTextLayouts(), after the existing topic ID validation, add:

if (!StringUtils.equalsOrBothEmpty(titleText, topic.info.name)) {
  return;
}

3. At the end of setTopic(), before invalidate(), add:

if (lastMeasuredWidth > 0) {
  buildTextLayouts();
}

4. In onDraw(), right after the null check, add:

if (topic.info.forumTopicId != currentTopicId || topic.info.chatId != currentChatId) {
  return;
}

Tested it and the issue is gone now

[LeeseTheFox]

And also, another bug: tapping on a Replies notification would open the @replies chat but show it as empty with just the "This chat helps you keep track of replies..." message, even though there were actual replies

The issue was in MainActivity.openMessagesController() - when the forum topics support was added, the code assumed all messageThreadId values were forum topic IDs and always created MessageTopicForum objects. But Replies use MessageTopicThread instead, so the app couldn't find the thread and showed the empty state.

Here's the fix for MainActivity.java:

In the openMessagesController() method, replace:

if (messageThreadId != 0) {
  params.messageTopic(new TdApi.MessageTopicForum((int) messageThreadId));
}

With:

if (messageThreadId != 0) {
  // Determine if this is a forum topic or message thread (Replies)
  // The @replies chat and non-forum supergroups use MessageTopicThread
  // Forum chats use MessageTopicForum
  if (tdlib.isRepliesChat(chatId) || tdlib.hasMessageThreads(chatId)) {
    // This is a message thread (Replies) in the @replies chat or a non-forum supergroup
    params.messageTopic(new TdApi.MessageTopicThread(messageThreadId));
  } else {
    // This is a forum topic
    params.messageTopic(new TdApi.MessageTopicForum((int) messageThreadId));
  }
}