perf(room): memoize timeline/composer handlers and emoji-pack room lookups

- RoomTimeline: wrap jump-to-latest/unread + mark-as-read handlers in useCallback
  (the handlers passed to memoized message children were already memoized).
- RoomInput: wrap file/upload/emoji/sticker/location callbacks in useCallback so
  the editor and toolbar don't re-render needlessly.
- EmojiBoard: hoist repeated mx.getRoom() pack-label lookups into a useMemo'd map
  in the emoji and sticker sidebars (previously called per-render in map loops).

Behavior unchanged. (RoomTimeline/RoomInput already have ErrorBoundary wrappers
in RoomView, so no boundary added.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/RoomTimeline.tsx

@@ -906,25 +906,25 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
     }
   }, [scrollToElement, editId]);
 
-  const handleJumpToLatest = () => {
+  const handleJumpToLatest = useCallback(() => {
     if (eventId) {
       navigateRoom(room.roomId, undefined, { replace: true });
     }
     setTimeline(getInitialTimeline(room));
     scrollToBottomRef.current.count += 1;
     scrollToBottomRef.current.smooth = false;
-  };
+  }, [eventId, navigateRoom, room]);
 
-  const handleJumpToUnread = () => {
+  const handleJumpToUnread = useCallback(() => {
     if (unreadInfo?.readUptoEventId) {
       setTimeline(getEmptyTimeline());
       loadEventTimeline(unreadInfo.readUptoEventId);
     }
-  };
+  }, [unreadInfo, loadEventTimeline]);
 
-  const handleMarkAsRead = () => {
+  const handleMarkAsRead = useCallback(() => {
     markAsRead(mx, room.roomId, hideActivity);
-  };
+  }, [mx, room, hideActivity]);
 
   const handleOpenReply: MouseEventHandler = useCallback(
     async (evt) => {