Read port forwards from per-VM forwards.conf files

A QEMU config file section cannot hold more than one hostfwd entry, so
the forwards move out of the ini files into qemu/<vm>/forwards.conf, one
"LABEL HOST_PORT GUEST_PORT" rule per line. The new vmforwards.py parses
them, skips rules whose host port is taken and builds the -netdev
argument, which every launcher now passes instead of relying on a
netdev section in the ini or on -nic.

The ini files move to qemu/<vm>/config.ini and qemu/<vm>/<os>-<arch>.ini.
The *_SSH_PORT / *_RDP_PORT variables and --rdp-port / --ssh-port still
replace the host port of the SSH and RDP rules.

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

qemu/windows11/linux-arm64.ini

@@ -0,0 +1,38 @@
+# Linux host, arm64 part of the Windows 11 QEMU configuration; read after config.ini.
+
+# Accelerators are tried in order: KVM on Linux, else emulation.
+[accel]
+  accel = "kvm"
+
+[accel]
+  accel = "tcg"
+
+[machine]
+  type = "virt"
+
+# The "virt" machine has no IDE. NVMe and USB mass storage (used by the
+# installation media of --install-from-iso) both have inbox Windows drivers.
+[device "system_disk-dev"]
+  driver = "nvme"
+  drive = "system_disk"
+  serial = "win11disk"
+  bootindex = "1"
+
+# Windows has no inbox driver for virtio-net; the guest tools installed by
+# Configure-Windows.ps1 provide it.
+[device "nic0"]
+  driver = "virtio-net-pci"
+  netdev = "net0"
+
+# Unlike q35, "virt" has no default GPU or keyboard. virtio-gpu is the only
+# display, driven by viogpudo (installed by Configure-Windows.ps1). ramfb is not
+# added because Windows would then see a second adapter with a fixed-mode
+# monitor. xres/yres set the preferred mode in the EDID (QEMU defaults to
+# 1280x800); viogpudo accepted 1920x1200 and 2048x1280 but not 2560x1600.
+[device "gpu0"]
+  driver = "virtio-gpu-pci"
+  xres = "2048"
+  yres = "1280"
+
+[device "kbd0"]
+  driver = "usb-kbd"