Column flex on keep-alive room hosts so the timeline fills the pane again, and route unicode jumbo through the plain emoji path with dedicated HTML parser options for custom emoticons.
- Enhance RoomInput to support sending messages as replies in threads by adding `threadRootId` prop.
- Update RoomTimeline to manage active thread state and handle opening threads.
- Implement ThreadView component to display thread messages and input.
- Create HomeThreadsCategory to list threads user has participated in.
- Introduce activeThreadIdAtomFamily to manage active thread state across rooms.
