fix(room): hoist mentionConfirmRef to module scope to fix TDZ error

ChatInputArea is defined before RoomChatPanel in the file, so its JSX
runs before mentionConfirmRef is declared inside RoomChatPanel. Moving the
ref to module level ensures it's initialized before either component renders.

src/components/room/RoomChatPanel.tsx

@@ -29,6 +29,8 @@ import { RoomThreadPanel } from './RoomThreadPanel';
 
 const MENTION_PATTERN = /@([^:@\s]*)(:([^\s]*))?$/;
 const MENTION_POPOVER_KEYS = ['Enter', 'Tab', 'ArrowUp', 'ArrowDown'];
+/** Module-level ref shared between ChatInputArea (writes) and RoomChatPanel (reads) */
+const mentionConfirmRef = { current: (() => {}) as () => void };
 
 export interface ChatInputAreaHandle {
   insertMention: (id: string, label: string, type: 'user' | 'ai') => void;
@@ -283,8 +285,6 @@ export function RoomChatPanel({ room, isAdmin, onClose, onDelete }: RoomChatPane
 
   const messagesEndRef = useRef<HTMLDivElement>(null);
   const chatInputRef = useRef<ChatInputAreaHandle>(null);
-  /** Shared ref: MentionPopover writes the confirm fn here; ChatInputArea reads and calls it */
-  const mentionConfirmRef = useRef<() => void>(() => {});
 
   const [replyingTo, setReplyingTo] = useState<MessageWithMeta | null>(null);
   const [editingMessage, setEditingMessage] = useState<MessageWithMeta | null>(null);