Room list: improve custom sections in Spaces (#33523)

* feat: display empty custom sections in the space where they were created

* test: update tests

* fix: room can't be drag in to a section if a section is created before

* fix: re-render issue when section is created

packages/shared-components/src/room-list/VirtualizedRoomListView/VirtualizedRoomListView.tsx

@@ -264,6 +264,8 @@ export function VirtualizedRoomListView({ vm, renderAvatar, onKeyDown }: Virtual
 
             return (
                 <RoomListSectionHeaderView
+                    // Stable key per section avoids a @dnd-kit registration race when a new section is inserted.
+                    key={headerId}
                     vm={sectionHeaderVM}
                     isFocused={isFocused}
                     onFocus={onFocus}