windows: seal mode -- generic OOBE-deferred base, per-VM data on a config CD

A sealed image bakes no per-VM data. generalize.nix gains a gated
configMedium flag (false path byte-identical, so the shared macOS
generalize path is untouched): the baked answer file stays generic and
the target's first boot reads hostname/static-IP/timezone/tint off a
small removable CD via a finder (vmix-load-config.cmd) + applier
(vmix-apply-config.ps1), with the static-IP script dot-sourcing the same
config. templates.seal is a thin preset (delayOobeRun + configMedium +
D:\Users profiles + a data disk); images gain a .seal leaf next to
.generalize; makeConfigMedium renders the per-VM ISO.

So one sealed store path is shared by every VM, each mints its own SID
on first boot and builds the whole profile on D:, and only a cheap ISO
is per-VM. Also folds in the delayOobeRun reconcile: extraDisk (and the
audit-mode data-disk init) are gated off under deferral, so a sealed
image ships with no throwaway `data` output -- the target's specialize
formats the host zvol instead.

vms: disks.config.file attaches the config medium as a second CD-ROM.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0117qMyjpuXsjpVAcpJbFD8g

nixos/vms/config.nix

@@ -241,6 +241,7 @@ let
           ''} \
           ${optionalString hasOsDisk "-drive file=${osDiskPath},format=qcow2,if=virtio${optionalString (vmCfg.disks.os.persist == false) ",snapshot=on"}"} \
           ${optionalString (vmCfg.disks.iso.file != null) "-drive file=${toString vmCfg.disks.iso.file},media=cdrom,readonly=on"} \
+          ${optionalString (vmCfg.disks.config.file != null) "-drive file=${toString vmCfg.disks.config.file},media=cdrom,readonly=on"} \
           ${concatMapStrings (diskCfg: ''
             -drive file=${toString diskCfg.file},format=${diskCfg.format},if=${vmCfg.disks.bus} \
           '') (attrValues vmCfg.disks.add)} \