feat(export): prioritize tab counts via lightweight api

electron/preload.ts

@@ -130,6 +130,7 @@ contextBridge.exposeInMainWorld('electronAPI', {
   chat: {
     connect: () => ipcRenderer.invoke('chat:connect'),
     getSessions: () => ipcRenderer.invoke('chat:getSessions'),
+    getExportTabCounts: () => ipcRenderer.invoke('chat:getExportTabCounts'),
     enrichSessionsContactInfo: (usernames: string[]) =>
       ipcRenderer.invoke('chat:enrichSessionsContactInfo', usernames),
     getMessages: (sessionId: string, offset?: number, limit?: number, startTime?: number, endTime?: number, ascending?: boolean) =>