Add linting, formatting, and CI with fixes for all warnings

Infrastructure:
- Add deadnix, nixfmt, and statix to flake inputs
- Add formatter output to flake for nix fmt support
- Add deadnix, nixfmt, statix to Home Manager packages
- Add GitHub Actions workflow for CI validation
- Add .pre-commit-config.yaml with hooks for nixfmt, deadnix, and statix
- Support x86_64-darwin in formatter

Statix fixes (W10/W20 warnings):
- Remove unused lambda argument from nixpkgs-settings.nix
- Merge repeated keys in hardware-configuration.nix files (boot.initrd, boot, fileSystems)
- Merge repeated keys in nixnuc/default.nix (services, virtualisation)
- Merge repeated keys in rainbow-planet/default.nix (desktopManager)
- Merge repeated keys in home/general/default.nix (home)

Deadnix fixes (unused declarations):
- Remove unused pkgs/lib/username/http_port arguments from various files
- Fix unused final parameter in overlay functions (final -> _final)

CI/pre-commit fixes:
- Fix pre-commit statix config: add pass_filenames: false
- Fix CI workflow: use nix run nixpkgs# prefix and --ci flag for nixfmt

modules/hosts/nixos/rainbow-planet/hardware-configuration.nix

@@ -1,36 +1,56 @@
 # 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, modulesPath, pkgs, ... }:
+{
+  config,
+  lib,
+  modulesPath,
+  ...
+}:
 
 {
-  imports =
-    [ (modulesPath + "/installer/scan/not-detected.nix")
-    ];
-
-  boot.initrd.availableKernelModules = [ "xhci_pci" "nvme" "usb_storage" "sd_mod" "rtsx_pci_sdmmc" ];
-  # boot.kernelPackages = pkgs.linuxPackages_zen;
-  boot.initrd.kernelModules = [ ];
-  boot.kernelModules = [ "kvm-intel" "sg" ];
-  boot.kernelParams = [
-    "i915.enable_fbc=1"
-    "i915.enable_psr=2"
+  imports = [
+    (modulesPath + "/installer/scan/not-detected.nix")
   ];
-  boot.extraModulePackages = [ ];
 
-  fileSystems."/" =
-    { device = "/dev/disk/by-uuid/eb9a2c7e-ae61-4d06-9464-49b98d576f7c";
+  boot = {
+    initrd = {
+      availableKernelModules = [
+        "xhci_pci"
+        "nvme"
+        "usb_storage"
+        "sd_mod"
+        "rtsx_pci_sdmmc"
+      ];
+      # boot.kernelPackages = pkgs.linuxPackages_zen;
+      kernelModules = [ ];
+    };
+    kernelModules = [
+      "kvm-intel"
+      "sg"
+    ];
+    kernelParams = [
+      "i915.enable_fbc=1"
+      "i915.enable_psr=2"
+    ];
+    extraModulePackages = [ ];
+  };
+
+  fileSystems = {
+    "/" = {
+      device = "/dev/disk/by-uuid/eb9a2c7e-ae61-4d06-9464-49b98d576f7c";
       fsType = "ext4";
     };
 
-  fileSystems."/boot" =
-    { device = "/dev/disk/by-uuid/924D-E7A4";
+    "/boot" = {
+      device = "/dev/disk/by-uuid/924D-E7A4";
       fsType = "vfat";
     };
+  };
 
-  swapDevices =
-    [ { device = "/dev/disk/by-uuid/166d24ca-401c-492e-845d-bb1d0d6d7d86"; }
-    ];
+  swapDevices = [
+    { device = "/dev/disk/by-uuid/166d24ca-401c-492e-845d-bb1d0d6d7d86"; }
+  ];
 
   # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
   # (the default) this is the recommended approach. When using systemd-networkd it's