Zoom the macOS display window to fit so the installer screen is usable on Retina

cocoa does not scale the guest by default, so the 1024x768 ramfb screen of the
Windows installer looks tiny on a Retina display. zoom-to-fit stretches it to
the window, as UTM does.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

run-windows11.py

@@ -138,7 +138,8 @@ Environment variables:
   WIN11_VM_UEFI_VARS    OVMF variable-store template path (auto-detected if unset)
   WIN11_VM_QEMU_CONFIG  QEMU config template passed to -readconfig
                         (default: qemu/windows11.ini)
-  WIN11_VM_DISPLAY      QEMU display backend (default: cocoa on macOS, gtk elsewhere)
+  WIN11_VM_DISPLAY      QEMU display backend (default: cocoa,zoom-to-fit=on on macOS,
+                        gtk elsewhere)
 """)
 
 
@@ -371,8 +372,11 @@ if installing:
              "-b", str(base_image), str(disk_image), disk_size])
     print(f"Created Windows 11 system disk: {disk_image}")
 
+# cocoa does not scale the guest by default, so the low-resolution installer
+# screen looks tiny on a Retina display; zoom-to-fit stretches it to the window,
+# as UTM does.
 display_backend = env("WIN11_VM_DISPLAY") or (
-    "cocoa" if platform.system() == "Darwin" else "gtk")
+    "cocoa,zoom-to-fit=on" if platform.system() == "Darwin" else "gtk")
 
 # Most of the VM definition lives in the QEMU config template; fill in the
 # file paths and hand the rendered file to QEMU with -readconfig.