refactor: restructure config files

modules/capabilities/networking.nix

@@ -0,0 +1,15 @@
+{
+  flake.modules.nixos.server-firewall = {
+    networking = {
+      firewall.enable = true;
+      firewall.allowPing = false;
+    };
+  };
+
+  flake.modules.nixos.networking = {
+    networking = {
+      nftables.enable = true;
+      networkmanager.enable = true;
+    };
+  };
+}