fix(mobile): make media gallery and members panel accessible on mobile

MediaGallery: fixed panel now goes full-width (100%) on mobile instead
of the inaccessible 320px right sidebar. Added 'Media Gallery' MenuItem
to RoomMenu (visible only on mobile) so users can open it from the
More Options (···) button.

MembersDrawer: removed ScreenSize.Desktop gate in Room.tsx so it now
renders on mobile too. CSS media query (≤750px) makes it position:fixed
inset:0 width:100% on mobile instead of the 266px desktop sidebar.
Added 'Members' MenuItem to RoomMenu for mobile access.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/MediaGallery.tsx

@@ -21,6 +21,7 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { decryptFile, downloadEncryptedMedia, mxcUrlToHttp } from '../../utils/matrix';
 import { ContainerColor } from '../../styles/ContainerColor.css';
+import { ScreenSize, useScreenSizeContext } from '../../hooks/useScreenSize';
 
 type GalleryTab = 'image' | 'video' | 'file';
 
@@ -531,6 +532,8 @@ type MediaGalleryProps = {
 export function MediaGallery({ room, onClose }: MediaGalleryProps) {
   const mx = useMatrixClient();
   const useAuthentication = useMediaAuthentication();
+  const screenSize = useScreenSizeContext();
+  const isMobile = screenSize === ScreenSize.Mobile;
 
   const [tab, setTab] = useState<GalleryTab>('image');
   const [loading, setLoading] = useState(false);
@@ -650,9 +653,9 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
           top: 0,
           right: 0,
           bottom: 0,
-          width: '320px',
+          width: isMobile ? '100%' : '320px',
           zIndex: 500,
-          borderLeft: `1px solid ${color.Surface.ContainerLine}`,
+          borderLeft: isMobile ? 'none' : `1px solid ${color.Surface.ContainerLine}`,
           overflow: 'hidden',
         }}
       >