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-status/MemberGlance.tsx

@@ -4,8 +4,8 @@ import React, { useState } from 'react';
 import FocusTrap from 'focus-trap-react';
 import { Room } from 'matrix-js-sdk';
 import { UserAvatar } from '../../components/user-avatar';
-import { getMemberAvatarMxc, getMemberDisplayName } from '../../utils/room';
-import { getMxIdLocalPart, mxcUrlToHttp } from '../../utils/matrix';
+import { getMemberAvatarMxc, getMemberName } from '../../utils/room';
+import { mxcUrlToHttp } from '../../utils/matrix';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { StackedAvatar } from '../../components/stacked-avatar';
@@ -128,7 +128,7 @@ export function MemberGlance({ room, members, speakers, callEmbed, max = 6 }: Me
         {visibleMembers.map((callMember) => {
           const { userId } = callMember;
           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)