feat: add proper QEMU guest support for memory ballooning

- Import NixOS qemu-guest.nix profile (sets up virtio modules in initrd)
- Enable qemu-guest-agent service for VM management
- Remove manual virtio_balloon config (now handled by profile)

The qemu-guest profile properly configures:
- virtio_balloon in boot.initrd.kernelModules (loads early)
- virtio_console, virtio_rng, virtio_gpu
- virtio_net, virtio_pci, virtio_blk, virtio_scsi

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

configuration.nix

@@ -2,12 +2,15 @@
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
 
-{ config, pkgs, ... }:
+{ config, pkgs, modulesPath, ... }:
 
 
 {
 
-    # imports = [ ./hw.nix ];
+  # Import NixOS QEMU guest profile for optimal virtio support
+  imports = [
+    "${modulesPath}/profiles/qemu-guest.nix"
+  ];
 
   # boot.loader.grub.device = "/dev/vda";
   # fileSystems."/" = {
@@ -20,8 +23,8 @@
     "console=tty1"
   ];
 
-  # Enable virtio balloon driver for dynamic memory resizing
+  # QEMU guest agent for VM management (memory stats, filesystem freeze, etc.)
-  boot.kernelModules = [ "virtio_balloon" ];
+  services.qemuGuest.enable = true;
 
   systemd.services."serial-getty@ttyS0" = {
     enable = true;