Detached sidebar cannot open external URLs or local file reviews

## Summary

When the sidebar is detached from the main Cindy window and opened as a separate window, content cannot be opened in that sidebar. This affects both external URLs and local file review links.

Moving the sidebar back into the main Cindy window immediately restores normal behavior.

## Steps to reproduce

1. Open Cindy.
2. Detach the sidebar so it is displayed in a separate window.
3. Click an external URL, for example: https://github.com/makecindy/cindy
4. Choose the option to open it in the sidebar.
5. Observe that the content does not open correctly.
6. Try to open a local file for review in the sidebar.
7. Observe the same failure.
8. Move the sidebar back into the main Cindy window and repeat either action.

## Actual behavior

External URLs and local file reviews cannot be opened in the sidebar while the sidebar is in a separate window.

## Expected behavior

"Open in sidebar" should work regardless of whether the sidebar is docked inside the main Cindy window or displayed in a separate window.

## Additional context

- Reproduced with both an external HTTPS URL and a local file review link.
- Docking the sidebar back into the Cindy main window consistently makes both actions work again.

Start by reproducing the failure and tracing the detached sidebar window's handling of the "Open in sidebar" action for both an external HTTPS URL and a local file review link. Done means both content types open correctly whether the sidebar is docked in the Cindy window or detached.

Written by the indexing model from the issue text.