Add Go compiler; split system.nix into focused modules

system.nix had grown to 200 lines covering boot, networking, locale,
audio, Bluetooth, fonts, nix settings, hardening, DNS and RGB. Split it
by concern into boot.nix, networking.nix, locale.nix, nix-settings.nix,
security.nix and audio.nix.

Also:
- drivers.nix -> hardware.nix, absorbing Bluetooth, the I2C udev rule,
  OpenRGB and printing
- fonts -> desktop.nix
- nix-ld and pkgs.file -> apps.nix
- the Bottles tmpfiles link -> users.nix, next to services.flatpak

The reorganization is behavior-neutral: the dbus-1, system-units,
user-units and system-path trees are byte-identical to the previous
build once self-referential store paths are normalized, and
`nix store diff-closures` against the running system reports exactly
one change -- go 1.26.7.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

modules/hardware.nix

@@ -0,0 +1,61 @@
+{ config, lib, pkgs, ... }:
+
+{
+  hardware.graphics = {
+    enable = true;
+    enable32Bit = true;
+  };
+
+  services.xserver.videoDrivers = [ "nvidia" ];
+
+  hardware.nvidia = {
+    modesetting.enable = true;
+    open = true;
+    nvidiaSettings = true;
+    package = config.boot.kernelPackages.nvidiaPackages.stable;
+  };
+
+  hardware.opentabletdriver.enable = true;
+  hardware.uinput.enable = true;
+  boot.kernelModules = [ "uinput" ];
+
+  hardware.bluetooth = {
+    enable = true;
+    powerOnBoot = true;
+    settings = {
+      General = {
+        Experimental = true;      # Battery level of connected devices
+        FastConnectable = true;   # Faster reconnects, more power draw
+      };
+      Policy = {
+        AutoEnable = true;
+      };
+    };
+  };
+  services.blueman.enable = true;
+
+  boot.extraModprobeConfig = ''
+    # DualSense/PS4 pads pair over Bluetooth then drop instantly; broken
+    # ERTM in many adapters. Disabling it is the standard fix.
+    options bluetooth disable_ertm=1
+  '';
+
+  # Blog V4 needs the rtlsdrblog fork of librtlsdr, which is what
+  # pkgs.rtl-sdr already is here. Also blacklists the DVB-T drivers.
+  hardware.rtl-sdr.enable = true;
+
+  # For ddcutil — no laptop backlight here, only external DisplayPort.
+  hardware.i2c.enable = true;
+
+  services.hardware.openrgb = {
+    enable = true;
+    motherboard = "amd";
+  };
+
+  services.udev.extraRules = ''
+    # OpenRGB
+    SUBSYSTEM=="i2c-dev", GROUP="i2c", MODE="0660"
+  '';
+
+  services.printing.enable = true;
+}