macOS: tab bar goes black in fullscreen after disconnecting the external display

1. Create a new window in an external display
2. Enter fullscreen there
3. Create new tabs in fullscreen
4. Disconnect that display

This is reproducible with both default config and macos-titlebar-style = tabs

Related discussion and pr:

• https://github.com/ghostty-org/ghostty/discussions/5389
• https://github.com/ghostty-org/ghostty/pull/10253
• https://github.com/ghostty-org/ghostty/pull/13407

I don't think the mentioned pr above are the right approach to fix it, but feel free to try them yourself.