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.

home/symlinks.nix

@@ -0,0 +1,10 @@
+{ config, lib, ... }:
+
+{
+  home.file = lib.mapAttrs'
+    (name: _: lib.nameValuePair ".config/${name}" {
+      source = config.lib.file.mkOutOfStoreSymlink
+        "${config.home.homeDirectory}/nixos-dotfiles/config/${name}";
+    })
+    (lib.filterAttrs (_: type: type == "directory") (builtins.readDir ../config));
+}