feat: 新增 laptop 主机配置（Ultra 9 285H / Arc）

- hosts/laptop/hardware.nix: 本机真实硬件配置（btrfs 子卷 / NPU / 微码）
- hosts/laptop/default.nix: 复用 common/desktop-plasma/chinese/gaming/printing/apps，跳过 nvidia 与 fpga；加 Intel Arc VA-API
- flake.nix: 抽出 mkSystem，新增 nixosConfigurations.laptop / nixos

hosts/laptop/hardware.nix

@@ -0,0 +1,46 @@
+# Do not modify this file!  It was generated by ‘nixos-generate-config’
+# and may be overwritten by future invocations.  Please make changes
+# to /etc/nixos/configuration.nix instead.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/installer/scan/not-detected.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "thunderbolt" "nvme" "uas" "sd_mod" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" =
+    { device = "/dev/disk/by-uuid/cbcb5930-50a9-4ff8-92f9-4622bd869579";
+      fsType = "btrfs";
+    };
+
+  fileSystems."/home" =
+    { device = "/dev/disk/by-uuid/cbcb5930-50a9-4ff8-92f9-4622bd869579";
+      fsType = "btrfs";
+      options = [ "subvol=home" ];
+    };
+
+  fileSystems."/nix" =
+    { device = "/dev/disk/by-uuid/cbcb5930-50a9-4ff8-92f9-4622bd869579";
+      fsType = "btrfs";
+      options = [ "subvol=nix" ];
+    };
+
+  fileSystems."/boot" =
+    { device = "/dev/disk/by-uuid/84D8-EB50";
+      fsType = "vfat";
+      options = [ "fmask=0077" "dmask=0077" ];
+    };
+
+  swapDevices =
+    [ { device = "/dev/disk/by-uuid/d62e342b-271a-40e7-912d-3a748b5f55a1"; }
+    ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+  hardware.cpu.intel.npu.enable = true;
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+}