PR triage: option to hide traffic lights on macOS (suggested in discussion #7331)

[danielwe]

I've implemented the feature requested in #7331: an option to hide the traffic light window buttons on macOS for a cleaner aesthetic. See branch/diff at main...danielwe:ghostty:hide-trafficlights

Would you welcome this as a PR?

This adds an extra config option, which I know isn't ideal, but seems inevitable as this feature is mostly orthogonal to other style preferences.

Note: there's some code sharing with #7496 for properly hiding the toolbar title when the tab bar is visible. I'll rebase as needed if both changes are accepted as PRs.

Screenshots:

With default titlebar style:

[mitchellh]

Yes this looks acceptable to me. Thank you!