Support arm64 hosts in the Windows 11 launcher

Pick qemu-system-aarch64, the AArch64 UEFI firmware and a per-architecture
QEMU config (NVMe disk, virtio-net, ramfb, USB installation media) on arm64,
render the answer file for the target architecture, and move the q35-only
disk and NIC devices out of the shared config. Update vm-images to match
arm64 Windows ISO names.

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

qemu/windows11.ini

@@ -1,5 +1,5 @@
 # QEMU configuration for the Windows 11 virtual machine. The machine type is in
-# windows11-amd64.ini, which QEMU reads after this file.
+# windows11-<arch>.ini, which QEMU reads after this file.
 #
 # run-windows11.py fills in the file path placeholders below, writes the result
 # to <state dir>/qemu.ini and passes it to QEMU with -readconfig. Options that
@@ -37,27 +37,15 @@
   format = "raw"
   file = "${uefi_vars}"
 
-# System disk. It is attached through IDE so that Windows can boot before the
-# VirtIO storage driver is installed; the installation media of
-# --install-from-iso use ide.1 to ide.3.
+# System disk image; the device that exposes it (and the NIC, which is
+# attached to the user-mode network "net0" that the launcher defines with
+# -netdev because a config file section cannot hold more than one hostfwd) is in
+# the architecture file.
 [drive "system_disk"]
   if = "none"
   format = "qcow2"
   file = "${disk_image}"
 
-[device "system_disk-dev"]
-  driver = "ide-hd"
-  drive = "system_disk"
-  bus = "ide.0"
-  bootindex = "1"
-
-# The NIC is attached to the user-mode network "net0", which the launcher
-# defines with -netdev because a config file section cannot hold more than one
-# hostfwd (Remote Desktop and SSH are both forwarded to the host).
-[device "nic0"]
-  driver = "e1000e"
-  netdev = "net0"
-
 # Host/guest clipboard integration through the SPICE vdagent channel.
 [device "virtio_serial"]
   driver = "virtio-serial-pci"