feat: add thread functionality to room features

- 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.

src/app/features/room/RoomInput.tsx

@@ -126,9 +126,11 @@ interface RoomInputProps {
   fileDropContainerRef: RefObject<HTMLElement>;
   roomId: string;
   room: Room;
+  /** When provided, all messages are sent as replies in this thread. */
+  threadRootId?: string;
 }
 export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
-  ({ editor, fileDropContainerRef, roomId, room }, ref) => {
+  ({ editor, fileDropContainerRef, roomId, room, threadRootId }, ref) => {
     const mx = useMatrixClient();
     const useAuthentication = useMediaAuthentication();
     const [enterForNewline] = useSetting(settingsAtom, 'enterForNewline');
@@ -388,13 +390,20 @@ export const RoomInput = forwardRef<HTMLDivElement, RoomInputProps>(
           content['m.relates_to'].rel_type = RelationType.Thread;
           content['m.relates_to'].is_falling_back = false;
         }
+      } else if (threadRootId) {
+        content['m.relates_to'] = {
+          rel_type: RelationType.Thread,
+          event_id: threadRootId,
+          is_falling_back: true,
+          'm.in_reply_to': { event_id: threadRootId },
+        };
       }
       mx.sendMessage(roomId, content as any);
       resetEditor(editor);
       resetEditorHistory(editor);
       setReplyDraft(undefined);
       sendTypingStatus(false);
-    }, [mx, roomId, editor, replyDraft, sendTypingStatus, setReplyDraft, isMarkdown, commands, autoConvertEmoticons]);
+    }, [mx, roomId, threadRootId, editor, replyDraft, sendTypingStatus, setReplyDraft, isMarkdown, commands, autoConvertEmoticons]);
 
     const handleKeyDown: KeyboardEventHandler = useCallback(
       (evt) => {