feat: add vm-guest and vm-9p-automount modules

modules/nixos/vm-guest.nix

@@ -0,0 +1,49 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+{
+  options = {
+    vm-guest = {
+      enable = lib.mkEnableOption "VM guest configuration";
+      headless = lib.mkOption {
+        type = lib.types.bool;
+        default = false;
+        description = "run without display, serial console only";
+      };
+    };
+  };
+
+  config = lib.mkIf config.vm-guest.enable {
+    services.qemuGuest.enable = true;
+    services.spice-vdagentd.enable = lib.mkIf (!config.vm-guest.headless) true;
+
+    boot.kernelParams = lib.mkIf config.vm-guest.headless [ "console=ttyS0,115200" ];
+
+    # 9p for host file mounting
+    boot.initrd.availableKernelModules = [
+      "9p"
+      "9pnet_virtio"
+    ];
+    boot.kernelModules = [
+      "9p"
+      "9pnet_virtio"
+    ];
+
+    networking = {
+      useDHCP = true;
+      firewall.allowedTCPPorts = [ 22 ];
+    };
+
+    security.sudo.wheelNeedsPassword = false;
+
+    environment.systemPackages = with pkgs; [
+      curl
+      wget
+      htop
+      sshfs
+    ];
+  };
+}