DP18: add useMemberAvatar hook and adopt it in reader avatars

Add a reactive `useMemberAvatar(room, userId, w?, h?, resize?)` hook
returning { name, avatarUrl }, standardizing the member name + avatar
trio and the RoomStateEvent.Members reactivity pattern (N6). Convert
ReadReceiptAvatars and EventReaders to render per-user avatars via a
small child component using the hook, preserving exact sizes, fallback
rendering, TDS pill/tooltip styling and behavior.

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

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

@@ -15,19 +15,32 @@ import FocusTrap from 'focus-trap-react';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
-import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
-import { getMemberDisplayName } from '../../utils/room';
-import { getMxIdLocalPart, mxcUrlToHttp } from '../../utils/matrix';
+import { getMemberName } from '../../utils/room';
 import { UserAvatar } from '../user-avatar';
 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 { useMemberAvatar } from '../../hooks/useMemberAvatar';
 import * as css from './ReadReceiptAvatars.css';
 
 const MAX_DISPLAY = 5;
 
+function ReceiptStackedAvatar({ room, userId }: { room: Room; userId: string }) {
+  const { name, avatarUrl } = useMemberAvatar(room, userId);
+  return (
+    <StackedAvatar title={name} variant="SurfaceVariant" size="200" radii="Pill">
+      <UserAvatar
+        userId={userId}
+        src={avatarUrl}
+        alt={name}
+        renderFallback={() => <Icon size="50" src={Icons.User} filled />}
+      />
+    </StackedAvatar>
+  );
+}
+
 export function ReadReceiptAvatars({
   room,
   eventId,
@@ -38,7 +51,6 @@ export function ReadReceiptAvatars({
   userIds: string[];
 }) {
   const mx = useMatrixClient();
-  const useAuthentication = useMediaAuthentication();
   const [open, setOpen] = useState(false);
   const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
   const modalStyle = useModalStyle(360);
@@ -53,7 +65,7 @@ export function ReadReceiptAvatars({
     const handleMembers: RoomStateEventHandlerMap[RoomStateEvent.Members] = (
       event,
       _state,
-      member
+      member,
     ) => {
       if (event.getRoomId() === room.roomId && userIds.includes(member.userId)) {
         forceUpdate();
@@ -72,7 +84,7 @@ export function ReadReceiptAvatars({
   const tooltipNames =
     userIds
       .slice(0, 5)
-      .map((id) => getMemberDisplayName(room, id) ?? getMxIdLocalPart(id) ?? id)
+      .map((id) => getMemberName(room, id))
       .join(', ') + (extra > 0 ? ` +${extra} more` : '');
 
   return (
@@ -117,29 +129,9 @@ export function ReadReceiptAvatars({
             gap: '0px',
           }}
         >
-          {displayed.map((userId) => {
-            const name = getMemberDisplayName(room, userId) ?? getMxIdLocalPart(userId) ?? userId;
-            const avatarMxc = room.getMember(userId)?.getMxcAvatarUrl();
-            const avatarUrl = avatarMxc
-              ? (mxcUrlToHttp(mx, avatarMxc, useAuthentication, 32, 32, 'crop') ?? undefined)
-              : undefined;
-            return (
-              <StackedAvatar
-                key={userId}
-                title={name}
-                variant="SurfaceVariant"
-                size="200"
-                radii="Pill"
-              >
-                <UserAvatar
-                  userId={userId}
-                  src={avatarUrl}
-                  alt={name}
-                  renderFallback={() => <Icon size="50" src={Icons.User} filled />}
-                />
-              </StackedAvatar>
-            );
-          })}
+          {displayed.map((userId) => (
+            <ReceiptStackedAvatar key={userId} room={room} userId={userId} />
+          ))}
           {extra > 0 && (
             <Text
               size="T200"