fix(window): make macOS project tabs native window tabs (#2123)

Project tabs in a window group are now one native AppKit tab group behind the
page's own tab bar, with AppKit's tab bar hidden. The group shares one frame and
enters full screen as a whole, so every tab shows the system window buttons in
the bar revealed with the menu bar, and tabs no longer lose their title bar
layout after leaving full screen.

This removes the full-screen auxiliary windows, the host handover on close, the
frame copying between hidden members and the window buttons drawn by the page.
The title bar releases the room kept for the window buttons in full screen.
Linux and Windows keep showing one member at a time.

src/features/app/closeGuard.ts

@@ -205,7 +205,6 @@ async function onCloseRequested(deps: CloseDeps): Promise<boolean> {
       deps,
     );
     if (!ok) await (ctx.quitting ? commands.appCancelQuit() : commands.windowGroupCancelClose());
-    else if (!ctx.quitting) await commands.windowGroupBeforeClose();
     return ok;
   } catch (e) {
     maybeEditorService()?.cancelClose?.();

src/features/settings/__tests__/contrast.test.ts

@@ -123,7 +123,7 @@ describe("theme tokens", () => {
  * on purpose: colours the user assigns (project and data source colours), the
  * platform's caption close and macOS window buttons, and the tint strength.
  */
-const INHERITED_FROM_BASE = /^--(project-color-|db-color-|caption-close-|fg-caption-close-|mac-window-|tint-strength$)/;
+const INHERITED_FROM_BASE = /^--(project-color-|db-color-|caption-close-|fg-caption-close-|tint-strength$)/;
 
 describe("palette themes", () => {
   const ISLANDS = ["light", "dark", "dark-hc"];