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/state/activeThread.ts

@@ -0,0 +1,11 @@
+import { atom } from 'jotai';
+import { atomFamily } from 'jotai/utils';
+
+/** Stores the active thread root event ID for a given room. `undefined` means no thread is open. */
+const createActiveThreadAtom = () => atom<string | undefined>(undefined);
+
+export type TActiveThreadAtom = ReturnType<typeof createActiveThreadAtom>;
+
+export const activeThreadIdAtomFamily = atomFamily<string, TActiveThreadAtom>(
+  createActiveThreadAtom
+);