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/call/CallMemberCard.tsx

@@ -5,9 +5,9 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { useOpenUserRoomProfile } from '../../state/hooks/userRoomProfile';
 import { SequenceCard } from '../../components/sequence-card';
-import { getMemberAvatarMxc, getMemberDisplayName } from '../../utils/room';
+import { getMemberAvatarMxc, getMemberName } from '../../utils/room';
 import { useRoom } from '../../hooks/useRoom';
-import { getMxIdLocalPart, mxcUrlToHttp } from '../../utils/matrix';
+import { mxcUrlToHttp } from '../../utils/matrix';
 import { UserAvatar } from '../../components/user-avatar';
 import { AvatarDecoration } from '../../components/avatar-decoration/AvatarDecoration';
 import { getMouseEventCords } from '../../utils/dom';
@@ -26,7 +26,7 @@ export function CallMemberCard({ member }: CallMemberCardProps) {
   const { userId } = member;
   if (!userId) return null;
 
-  const name = getMemberDisplayName(room, userId) ?? getMxIdLocalPart(userId) ?? userId;
+  const name = getMemberName(room, userId);
   const avatarMxc = getMemberAvatarMxc(room, userId);
   const avatarUrl = avatarMxc
     ? (mxcUrlToHttp(mx, avatarMxc, useAuthentication, 96, 96) ?? undefined)