revert to pure sddm & peach: add ddc support

system/hosts/peach/default.nix

@@ -1,4 +1,8 @@
-{pkgs, ...}: {
+{
+  pkgs,
+  config,
+  ...
+}: {
   boot.kernelParams = ["appledrm.show_notch=1"];
 
   catppuccin = {
@@ -6,7 +10,19 @@
     flavor = "macchiato";
   };
 
-  services.displayManager.gdm.enable = true;
+  environment.systemPackages = with pkgs; [
+    ddcutil
+  ];
+
+  boot.extraModulePackages = [config.boot.kernelPackages.ddcci-driver];
+  boot.kernelModules = [
+    "i2c-dev"
+    "ddcci_backlight"
+  ];
+  services.udev.extraRules = ''
+    KERNEL=="i2c-[0-9]*", GROUP="i2c", MODE="0660"
+  '';
+  hardware.i2c.enable = true;
 
   hardware.asahi = {
     enable = true;