Appends the desktop theme toggle to a tab strip, once.
Guarded against duplicates: the tab strip is rebuilt whenever the registry changes, and a
second toggle would both render twice and double-fire the theme change.
⚠️ Appends the button ONLY. The separator is a layout anchor with its own lifetime and is
posted unconditionally by appendTabsSeparator — call that one first, and call it
even when this one is gated off by ui.showPanelThemeToggle.
Appends the desktop theme toggle to a tab strip, once.
Guarded against duplicates: the tab strip is rebuilt whenever the registry changes, and a second toggle would both render twice and double-fire the theme change.
⚠️ Appends the button ONLY. The separator is a layout anchor with its own lifetime and is posted unconditionally by appendTabsSeparator — call that one first, and call it even when this one is gated off by
ui.showPanelThemeToggle.