Selected thread persists across tabs

The selected thread appears to be persisted across tabs. Selected thread should be specific to the tab.

1. Open two tabs
2. Select a thread in tab 1
3. Observe that in tab 2, the main section's thread is now tab 1's thread. Sidebar shows the previously selected thread.
https://github.com/user-attachments/assets/67a07cf5-ad70-453f-88e0-cc5d67de391b