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/MembersDrawer.css.ts

@@ -3,6 +3,14 @@ import { config, toRem } from 'folds';
 
 export const MembersDrawer = style({
   width: toRem(266),
+  '@media': {
+    '(max-width: 750px)': {
+      position: 'fixed',
+      inset: 0,
+      width: '100%',
+      zIndex: 500,
+    },
+  },
 });
 
 export const MembersDrawerHeader = style({