add nicModel option to customizeImage and generalize

Allows overriding the QEMU NIC model during builds (e.g. e1000 for
images without VirtIO drivers). Enables MAS activation on upstream
images that lack VirtIO network drivers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/images/windows/helpers/customizeImage.nix

@@ -24,6 +24,7 @@
     vncDisplay ? null,
     smp ? 4,
     memSize ? 4096,
+    nicModel ? null,
   }:
   let
     originalImageName = lib.strings.removeSuffix "-vmix" (lib.strings.removeSuffix ".qcow2" originalImage.name);
@@ -104,7 +105,7 @@
           then "-drive file=${resultImg},format=qcow2,if=none,id=disk0 -device ide-hd,drive=disk0"
           else "-drive file=${resultImg},format=qcow2,if=virtio"} \
         ${cdromArgs} \
-        -nic user,model=${if isAHCI then "e1000" else "virtio-net-pci"}"
+        -nic user,model=${if nicModel != null then nicModel else if isAHCI then "e1000" else "virtio-net-pci"}"
 
       timeout 1800 qemu-system-x86_64 $VMIX_DISPLAY $QEMU_ARGS || \
         if [[ "$VMIX_DISPLAY" == "-display sdl" ]]; then