DP18: add getMemberName helper and dedup name-fallback sites

Add a pure `getMemberName(room, userId): string` helper in utils/room.ts
(= getMemberDisplayName ?? getMxIdLocalPart ?? userId) and replace the
inline `getMemberDisplayName(room, id) ?? getMxIdLocalPart(id) ?? id`
fallback across the codebase. No behavior change.

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

src/app/features/room/MembersDrawer.tsx

@@ -42,7 +42,7 @@ import {
 } from '../../hooks/useAsyncSearch';
 import { useDebounce } from '../../hooks/useDebounce';
 import { TypingIndicator } from '../../components/typing-indicator';
-import { getMemberDisplayName, getMemberSearchStr } from '../../utils/room';
+import { getMemberName, getMemberSearchStr } from '../../utils/room';
 import { getMxIdLocalPart } from '../../utils/matrix';
 import { useSetSetting, useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
@@ -134,8 +134,7 @@ function MemberItem({
   typing,
   showEncryption,
 }: MemberItemProps) {
-  const name =
-    getMemberDisplayName(room, member.userId) ?? getMxIdLocalPart(member.userId) ?? member.userId;
+  const name = getMemberName(room, member.userId);
   const avatarMxcUrl = member.getMxcAvatarUrl();
   const avatarUrl = avatarMxcUrl
     ? mx.mxcUrlToHttp(avatarMxcUrl, 100, 100, 'crop', undefined, false, useAuthentication)
@@ -418,10 +417,7 @@ export function MembersDrawer({ room, members }: MembersDrawerProps) {
                   Pending Requests
                 </Text>
                 {knockMembers.map((knockMember) => {
-                  const knockName =
-                    getMemberDisplayName(room, knockMember.userId) ??
-                    getMxIdLocalPart(knockMember.userId) ??
-                    knockMember.userId;
+                  const knockName = getMemberName(room, knockMember.userId);
                   const knockAvatarMxc = knockMember.getMxcAvatarUrl();
                   const knockAvatarUrl = knockAvatarMxc
                     ? mx.mxcUrlToHttp(