feat(dashboard): add moderation log page + message edit history

- Backend moderation module: GET /api/moderation/stats (per-status + failed rate)
  + GET /api/moderation/actions (filter by status/actionType, cursor paging),
  joins messages for target username + content
- Message GET /api/messages/detail/:id now returns edit_count + edit_history
  (old_content snapshots from message_edits, newest first)
- FE: new /moderation page — summary cards (total/executed/failed/pending +
  failed-rate), status+type filter chips, timeline rows with action icon,
  target user, reason, status badge, timestamps, error text
- FE: message detail shows 'Riwayat edit' panel with previous versions

services/backend/src/modules/messages/messages.service.ts

@@ -34,7 +34,12 @@ export class MessagesService {
       throw new NotFoundError(`Message with ID ${id} not found`);
     }
 
-    return message;
+    const editHistory = await messagesRepository.getEditHistory(id);
+    return {
+      ...message,
+      edit_count: editHistory.length,
+      edit_history: editHistory,
+    };
   }
 
   async getAttachmentsByChannel(channelId: string, query: MessageQuery) {