fix(bug,perf): poll first-vote race, stale timeline ref, lazy GifPicker/EmojiBoard, focusItem timer leak, RoomNavItem memo

BUG-18: clearTimeout cleanup in focusItem useLayoutEffect prevents leaked timers
BUG-24: Room timeline listener catches first poll vote before Relations object exists
BUG-25: Use timelineRef.current in handleOpenEvent to prevent stale index on rapid navigation
Perf-6: React.lazy + Suspense for GifPicker and EmojiBoard (initial bundle -114 kB)
Perf-7: React.memo on RoomNavItem to prevent re-renders on unrelated state

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

src/app/features/room-nav/RoomNavItem.tsx

@@ -245,7 +245,7 @@ type RoomNavItemProps = {
   showAvatar?: boolean;
   direct?: boolean;
 };
-export function RoomNavItem({
+function RoomNavItem_({
   room,
   selected,
   showAvatar,
@@ -440,3 +440,4 @@ export function RoomNavItem({
     </NavItem>
   );
 }
+export const RoomNavItem = React.memo(RoomNavItem_);