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/boot.nix

@@ -0,0 +1,39 @@
+{ config, lib, pkgs, ... }:
+
+{
+  boot.loader.efi.canTouchEfiVariables = true;
+  boot.loader.limine = {
+    enable = true;
+    maxGenerations = 5;
+
+    # Gruvbox, to match the icon theme.
+    style = {
+      wallpapers = [ ];   # Solid background; a path here would be used instead
+      interface = {
+        branding = "NixOS";
+        brandingColor = "fabd2f";
+        helpColor = "928374";
+        helpColorBright = "d79921";
+      };
+      graphicalTerminal = {
+        foreground = "ebdbb2";
+        background = "00282828";
+        brightForeground = "fbf1c7";
+        palette = "282828;cc241d;98971a;d79921;458588;b16286;689d6a;a89984";
+        brightPalette = "928374;fb4934;b8bb26;fabd2f;83a598;d3869b;8ec07c;ebdbb2";
+        margin = 32;
+      };
+    };
+  };
+
+  boot.kernelPackages = pkgs.linuxPackages;
+  boot.supportedFilesystems = [ "fuse" ];
+  programs.fuse.userAllowOther = true;
+
+  # zram instead of disk swap: nothing sensitive is written to disk in
+  # plaintext. systemd's gpt-auto-generator would otherwise re-activate the
+  # old swap partition regardless of swapDevices, hence the kernel param.
+  zramSwap.enable = true;
+  swapDevices = lib.mkForce [ ];
+  boot.kernelParams = [ "systemd.gpt_auto=0" "acpi_enforce_resources=lax" ];
+}