refactor: optimize flake.nix and modularize networking config

Cleaner deploy.nodes generation, improved devShell experience, and centralized host IP definitions using utils.lib.system variables.

modules/common/default.nix

@@ -1,4 +1,9 @@
 {
+  imports = [
+    ./networking.nix
+    ./secrets.nix
+  ];
+
   config = {
     homelab = {
       services.openssh.enable = true;

modules/common/networking.nix

@@ -0,0 +1,19 @@
+{ config, lib, ... }:
+
+{
+  options.homelab.networking = {
+    hostIp = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      description = ''
+        The primary IP address of the host. 
+        Used for automated deployment and internal service discovery.
+      '';
+    };
+  };
+
+  config = lib.mkIf (config.homelab.networking.hostIp != null) {
+    # If a hostIp is provided, we can potentially use it to configure 
+    # networking interfaces or firewall rules automatically here in the future.
+  };
+}