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/post-install/monitoring.nix

@@ -1,6 +1,8 @@
-{ config, pkgs, ... }: let
+{ config, pkgs, ... }:
+let
   metrics_server = "https://monitoring.home.technicalissues.us/remotewrite";
-in {
+in
+{
   services = {
     vmagent = {
       enable = true;
@@ -14,11 +16,11 @@ in {
           {
             job_name = "node";
             static_configs = [
-              { targets = ["127.0.0.1:9100"]; }
+              { targets = [ "127.0.0.1:9100" ]; }
             ];
             metric_relabel_configs = [
               {
-                source_labels = ["__name__"];
+                source_labels = [ "__name__" ];
                 regex = "go_.*";
                 action = "drop";
               }
@@ -35,11 +37,11 @@ in {
           {
             job_name = "nginx";
             static_configs = [
-              { targets = ["127.0.0.1:9113"]; }
+              { targets = [ "127.0.0.1:9113" ]; }
             ];
             metric_relabel_configs = [
               {
-                source_labels = ["__name__"];
+                source_labels = [ "__name__" ];
                 regex = "go_.*";
                 action = "drop";
               }
@@ -77,7 +79,7 @@ in {
     # ----------------------------
     # Exporters (using built-in NixOS modules)
     # ----------------------------
-    
+
     # Node exporter - using the built-in module
     prometheus.exporters.node = {
       enable = true;
@@ -110,7 +112,7 @@ in {
     group = "vmagent";
   };
 
-  users.groups.vmagent = {};
+  users.groups.vmagent = { };
 
   # ----------------------------
   # SOPS secrets configuration
@@ -119,10 +121,9 @@ in {
     secrets = {
       vmagent_push_pw = {
         owner = "vmagent";
-        restartUnits = ["vmagent.service"];
+        restartUnits = [ "vmagent.service" ];
         sopsFile = ../../../../shared/secrets.yaml;
       };
     };
   };
 }
-