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/RoomTimeline.tsx

@@ -543,6 +543,8 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
   const [timeline, setTimeline] = useState<Timeline>(() =>
     eventId ? getEmptyTimeline() : getInitialTimeline(room)
   );
+  const timelineRef = React.useRef(timeline);
+  timelineRef.current = timeline;
   const eventsLength = getTimelinesEventsCount(timeline.linkedTimelines);
   const liveTimelineLinked =
     timeline.linkedTimelines[timeline.linkedTimelines.length - 1] === getLiveTimeline(room);
@@ -659,7 +661,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
     ) => {
       const evtTimeline = getEventTimeline(room, evtId);
       const absoluteIndex =
-        evtTimeline && getEventIdAbsoluteIndex(timeline.linkedTimelines, evtTimeline, evtId);
+        evtTimeline && getEventIdAbsoluteIndex(timelineRef.current.linkedTimelines, evtTimeline, evtId);
 
       if (typeof absoluteIndex === 'number') {
         const scrolled = scrollToItem(absoluteIndex, {
@@ -678,7 +680,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
         loadEventTimeline(evtId);
       }
     },
-    [room, timeline, scrollToItem, loadEventTimeline]
+    [room, scrollToItem, loadEventTimeline]
   );
 
   useLiveTimelineRefresh(
@@ -847,13 +849,14 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
       });
     }
 
-    setTimeout(() => {
+    const timer = setTimeout(() => {
       if (!alive()) return;
       setFocusItem((currentItem) => {
         if (currentItem === focusItem) return undefined;
         return currentItem;
       });
     }, 2000);
+    return () => clearTimeout(timer);
   }, [alive, focusItem, scrollToItem]);
 
   // scroll to bottom of timeline