fix(receipts): refresh read-receipt avatars/names on member changes (N6)

ReadReceiptAvatars read avatar + display-name from room member state at render
time, so they only refreshed when the parent Message re-rendered (on a receipt
change). A reader changing their avatar/display-name left a stale avatar/name
until an unrelated re-render. Subscribe to RoomStateEvent.Members (the only signal
that fires for name, avatar AND membership changes — RoomMemberEvent has no Avatar
event) scoped to the displayed readers, and force a re-render so the pill updates
live. Listener is cleaned up; userIds identity is stable (memoized in the read-
positions map) so no subscribe churn.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/components/read-receipt-avatars/ReadReceiptAvatars.tsx

@@ -1,5 +1,5 @@
-import React, { useState } from 'react';
+import React, { useEffect, useState } from 'react';
-import { Room } from 'matrix-js-sdk';
+import { Room, RoomStateEvent, RoomStateEventHandlerMap } from 'matrix-js-sdk';
 import {
   Icon,
   Icons,
@@ -23,6 +23,7 @@ import { StackedAvatar } from '../stacked-avatar';
 import { EventReaders } from '../event-readers';
 import { stopPropagation } from '../../utils/keyboard';
 import { useModalStyle } from '../../hooks/useModalStyle';
+import { useForceUpdate } from '../../hooks/useForceUpdate';
 import * as css from './ReadReceiptAvatars.css';
 
 const MAX_DISPLAY = 5;
@@ -41,6 +42,28 @@ export function ReadReceiptAvatars({
   const [open, setOpen] = useState(false);
   const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
   const modalStyle = useModalStyle(360);
+  const [, forceUpdate] = useForceUpdate();
+
+  // The avatars + names below are read from room member state at render time, so
+  // they only refresh when this component re-renders (which the timeline does on a
+  // receipt change). Re-render on a member-state change of any displayed reader so
+  // an avatar/display-name update shows live. RoomStateEvent.Members fires for name,
+  // avatar AND membership changes (RoomMemberEvent has no Avatar signal).
+  useEffect(() => {
+    const handleMembers: RoomStateEventHandlerMap[RoomStateEvent.Members] = (
+      event,
+      _state,
+      member
+    ) => {
+      if (event.getRoomId() === room.roomId && userIds.includes(member.userId)) {
+        forceUpdate();
+      }
+    };
+    mx.on(RoomStateEvent.Members, handleMembers);
+    return () => {
+      mx.removeListener(RoomStateEvent.Members, handleMembers);
+    };
+  }, [mx, room.roomId, userIds, forceUpdate]);
 
   if (userIds.length === 0) return null;