Split configuration.nix and home.nix into per-domain modules

Break the two monolithic files into focused modules under system/
and home/ so each concern (boot, networking, xserver, picom, zsh,
git, rofi, etc.) lives in its own file. Clean up duplicates: drop
rofi from home.packages since programs.rofi.enable already installs
it, and move user-only apps (alacritty, obsidian, claude-code) from
environment.systemPackages to home.packages. Remove commented-out
boilerplate carried over from the install template.

system/xserver.nix

@@ -0,0 +1,28 @@
+{ ... }:
+
+{
+  services.xserver = {
+    enable = true;
+    autoRepeatDelay = 200;
+    autoRepeatInterval = 35;
+    windowManager.qtile.enable = true;
+    displayManager.sessionCommands = ''
+      xwallpaper --zoom ~/nixos-dotfiles/Pictures/NixOsWallpaper.png
+    '';
+    xrandrHeads = [
+      {
+        output = "HDMI-1";
+        monitorConfig = ''
+          Option "Position" "0 0"
+        '';
+      }
+      {
+        output = "DP-1";
+        primary = true;
+        monitorConfig = ''
+          Option "Position" "1920 0"
+        '';
+      }
+    ];
+  };
+}