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/shared/home/linux/apps/xfce4-terminal.nix

@@ -1,4 +1,4 @@
-{ ... }: {
+{
   home.file = {
     ".config/xfce4/terminal/accels.scm".source = ../../../files/xfce4/terminal/accels.scm;
   };
@@ -11,7 +11,8 @@
       "color-background" = "#08052b";
       "color-cursor" = "#ff7f7f";
       "color-cursor-use-default" = false;
-      "color-palette" = "#000000;#e52222;#a6e32d;#fc951e;#c48dff;#fa2573;#67d9f0;#f2f2f2;#555555;#ff5555;#55ff55;#ffff55;#5555ff;#ff55ff;#55ffff;#ffffff";
+      "color-palette" =
+        "#000000;#e52222;#a6e32d;#fc951e;#c48dff;#fa2573;#67d9f0;#f2f2f2;#555555;#ff5555;#55ff55;#ffff55;#5555ff;#ff55ff;#55ffff;#ffffff";
       "font-name" = "Hack Nerd Font Mono 12";
       "misc-always-show-tabs" = false;
       "misc-bell" = false;
@@ -43,4 +44,4 @@
       "title-initial" = "xfce4-terminal";
     };
   };
-}
+}