feat(ws-client): add TypingStart/TypingStop protocol types and client handlers

ws-protocol.ts: TypingStartPayload/TypingStopPayload interfaces,
WsEventPayload union types.

room-ws-client.ts: onTypingStart/onTypingStop callbacks, sendTyping()
method, event dispatch for typing.start/typing_start.

editor/types.ts: special_here/special_channel MentionType + description
field on MentionItem.

src/components/room/message/editor/types.ts

@@ -2,13 +2,14 @@
  * Core types for the IM editor (mentions, files, emojis).
  */
 
-export type MentionType = 'user' | 'channel' | 'ai' | 'command';
+export type MentionType = 'user' | 'channel' | 'ai' | 'command' | 'special_here' | 'special_channel';
 
 export interface MentionItem {
   id: string;
   label: string;
   type: MentionType;
   avatar?: string;
+  description?: string; // shown under label in suggestion dropdown
 }
 
 export interface FileData {

src/lib/room-ws-client.ts

@@ -78,6 +78,8 @@ export interface RoomWsCallbacks {
   onMessagePinned?: (payload: import('./ws-protocol').MessagePinnedPayload) => void;
   onMessageUnpinned?: (payload: import('./ws-protocol').MessageUnpinnedPayload) => void;
   onUserPresence?: (payload: UserPresencePayload) => void;
+  onTypingStart?: (payload: import('./ws-protocol').TypingStartPayload) => void;
+  onTypingStop?: (payload: import('./ws-protocol').TypingStopPayload) => void;
   onStatusChange?: (status: RoomWsStatus) => void;
   onError?: (error: Error) => void;
   /** Called each time the client sends a heartbeat ping */
@@ -961,6 +963,14 @@ export class RoomWsClient {
     return url;
   }
 
+  /** Send a typing_start / typing_stop event directly via WebSocket push (no response needed). */
+  sendTyping(roomId: string, action: 'start' | 'stop'): void {
+    if (this.ws && this.status === 'open') {
+      const event = { type: 'event', event: `typing_${action}`, room_id: roomId };
+      this.ws.send(JSON.stringify(event));
+    }
+  }
+
   private handleMessage(rawText: string): void {
     // Handle raw JSON pong before full parsing — resets heartbeat
     if (rawText.trim() === '{"type":"pong"}') {
@@ -1033,6 +1043,22 @@ export class RoomWsClient {
           status: ((event.data as { status?: string })?.status ?? 'offline') as 'online' | 'away' | 'dnd' | 'offline',
         });
         break;
+      case 'typing.start':
+      case 'typing_start':
+        this.callbacks.onTypingStart?.({
+          room_id: event.room_id ?? '',
+          user_id: (event.data as { user_id?: string })?.user_id ?? '',
+          username: (event.data as { username?: string })?.username ?? '',
+          avatar_url: (event.data as { avatar_url?: string })?.avatar_url,
+        });
+        break;
+      case 'typing.stop':
+      case 'typing_stop':
+        this.callbacks.onTypingStop?.({
+          room_id: event.room_id ?? '',
+          user_id: (event.data as { user_id?: string })?.user_id ?? '',
+        });
+        break;
       default:
         // Unknown event type - ignore silently
         break;

src/lib/ws-protocol.ts

@@ -133,7 +133,20 @@ export type WsResponseData =
   | NotificationListData
   | MentionListData
   | SubscribeData
-  | UserInfo[];
+  | UserInfo[]
+  | null;
+
+export interface TypingStartPayload {
+  room_id: string;
+  user_id: string;
+  username: string;
+  avatar_url?: string;
+}
+
+export interface TypingStopPayload {
+  room_id: string;
+  user_id: string;
+}
 
 export interface WsEvent {
   type: 'event';
@@ -155,6 +168,8 @@ export type WsEventPayload =
   | { type: 'message_pinned'; data: MessagePinnedPayload }
   | { type: 'message_unpinned'; data: MessageUnpinnedPayload }
   | { type: 'user_presence'; data: UserPresencePayload }
+  | { type: 'typing_start'; data: TypingStartPayload }
+  | { type: 'typing_stop'; data: TypingStopPayload }
   | { type: string; data: unknown }; // catch-all for unknown events
 
 export interface RoomMessagePayload {