fix(mobile): member list no longer opens on top of every room on phones (#175)

Room.tsx showed the MembersDrawer on phone widths whenever the persisted
desktop preference isPeopleDrawer was true — which is the default — so a
new mobile session opened every room behind a full-screen member list.
Mobile now uses a transient mobileMembersPanelAtom (header ⋮ → Members
toggles it, the drawer's X closes it, leaving the room resets it); the
desktop drawer keeps using the setting. Verified with Playwright at 400px.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/MembersDrawer.tsx

@@ -31,6 +31,8 @@ import { MatrixClient, Room, RoomMember } from 'matrix-js-sdk';
 import { useVirtualizer } from '@tanstack/react-virtual';
 import classNames from 'classnames';
 import { useSetAtom } from 'jotai';
+import { mobileMembersPanelAtom } from '../../state/mobileMembersPanel';
+import { ScreenSize, useScreenSizeContext } from '../../hooks/useScreenSize';
 import { MobileTouchTarget } from '../../styles/mobile.css';
 import { Membership } from '../../../types/matrix/room';
 
@@ -79,6 +81,8 @@ type MemberDrawerHeaderProps = {
 };
 function MemberDrawerHeader({ room }: MemberDrawerHeaderProps) {
   const setPeopleDrawer = useSetSetting(settingsAtom, 'isPeopleDrawer');
+  const setMobileMembers = useSetAtom(mobileMembersPanelAtom);
+  const screenSize = useScreenSizeContext();
 
   return (
     <Header className={css.MembersDrawerHeader} variant="Background" size="600">
@@ -104,7 +108,10 @@ function MemberDrawerHeader({ room }: MemberDrawerHeaderProps) {
                 ref={triggerRef}
                 variant="Background"
                 aria-label="Close member list"
-                onClick={() => setPeopleDrawer(false)}
+                onClick={() => {
+                  if (screenSize === ScreenSize.Mobile) setMobileMembers(false);
+                  else setPeopleDrawer(false);
+                }}
               >
                 <Icon src={Icons.Cross} />
               </IconButton>