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/hetznix01/default.nix

@@ -1,4 +1,9 @@
-{ inputs, pkgs, username,  ... }: {
+{
+  pkgs,
+  username,
+  ...
+}:
+{
   imports = [
     ../../../shared/nixos/nixroutes.nix
     ./disk-config.nix
@@ -24,14 +29,14 @@
   networking = {
     # Open ports in the firewall.
     firewall.allowedTCPPorts = [
-      22   # ssh
-      25   # SMTP (unencrypted)
-      80   # http to local Nginx
-      143  # imap
-      443  # https to local Nginx
-      465  # SMTP with TLS
-      587  # SMTP with STARTTLS
-      993  # imaps
+      22 # ssh
+      25 # SMTP (unencrypted)
+      80 # http to local Nginx
+      143 # imap
+      443 # https to local Nginx
+      465 # SMTP with TLS
+      587 # SMTP with STARTTLS
+      993 # imaps
       1883 # mqtt
       8333 # Bitcoin Core
       8448 # Matrix Synapse
@@ -88,7 +93,10 @@
   users.users.${username} = {
     isNormalUser = true;
     description = "Gene Liverman";
-    extraGroups = [ "networkmanager" "wheel" ];
+    extraGroups = [
+      "networkmanager"
+      "wheel"
+    ];
     linger = true;
   };
 }