feat: add status dashboard for live agent monitoring

Dedicated Discord channel shows per-group agent status with live
elapsed time. Single message is edited every 10s instead of spamming.

- GroupQueue tracks startedAt timestamps and exposes getStatuses()
- Channel interface gets editMessage/sendAndTrack for message editing
- STATUS_CHANNEL_ID env var to configure the dashboard channel
- Shows processing/idle/waiting/inactive per registered group

src/types.ts

@@ -74,6 +74,9 @@ export interface Channel {
   disconnect(): Promise<void>;
   // Optional: typing indicator. Channels that support it implement it.
   setTyping?(jid: string, isTyping: boolean): Promise<void>;
+  // Optional: edit/delete messages (used by status dashboard).
+  editMessage?(jid: string, messageId: string, text: string): Promise<void>;
+  sendAndTrack?(jid: string, text: string): Promise<string | null>;
   // Optional: sync group/chat names from the platform.
   syncGroups?(force: boolean): Promise<void>;
 }