feat(deploy): add batm3-installed NixOS config

HP ProDesk 600 G3 DM hardware module (temporary board replacement for
BATM3). Includes batm3-installed nixosConfiguration with auto-upgrade,
cachix, and systemd-boot.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/nixos/hardware/batm3.nix

@@ -0,0 +1,76 @@
+# BATM3 Hardware Configuration
+# HP ProDesk 600 G3 DM, Intel i5-7500T, Intel HD 630
+# Temporary board replacement for GeneralBytes BATM3 (ARM Android → x86 NixOS)
+
+{ config, lib, pkgs, ... }:
+
+{
+  boot = {
+    loader = {
+      systemd-boot.enable = true;
+      efi.canTouchEfiVariables = true;
+      timeout = 3;
+    };
+
+    initrd.availableKernelModules = [
+      "xhci_pci"
+      "ahci"
+      "usbhid"
+      "sd_mod"
+    ];
+
+    kernelModules = [
+      "kvm-intel"
+    ];
+
+    kernelParams = [
+      "quiet"
+      "splash"
+    ];
+  };
+
+  # Disk layout: GPT with ESP (sda1) + ext4 root (sda2)
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+  };
+
+  fileSystems."/boot" = {
+    device = "/dev/disk/by-label/ESP";
+    fsType = "vfat";
+  };
+
+  hardware = {
+    opengl = {
+      enable = true;
+      extraPackages = with pkgs; [
+        intel-media-driver
+        vaapiIntel
+        vaapiVdpau
+        libvdpau-va-gl
+      ];
+    };
+    enableRedistributableFirmware = true;
+    cpu.intel.updateMicrocode = true;
+  };
+
+  powerManagement = {
+    enable = true;
+    cpuFreqGovernor = "performance";
+  };
+
+  # Disable suspend/hibernate for kiosk
+  systemd.targets = {
+    sleep.enable = false;
+    suspend.enable = false;
+    hibernate.enable = false;
+    hybrid-sleep.enable = false;
+  };
+
+  # Serial port access for bill validator/dispenser (USB-serial adapters)
+  services.udev.extraRules = lib.mkAfter ''
+    KERNEL=="ttyS[0-9]*", MODE="0666"
+    KERNEL=="ttyUSB[0-9]*", MODE="0666"
+    KERNEL=="ttyACM[0-9]*", MODE="0666"
+  '';
+}