refactor: move host-specific settings to hosts directory

- Move defaultNameServers from network/dns.nix to hosts/servers/default.nix and hosts/workstations/default.nix
- Move SMTP configuration from network/smtp.nix to hosts/servers/default.nix and hosts/workstations/default.nix
- Move proxy configuration from network/proxy.nix to hosts/servers/default.nix and hosts/workstations/default.nix
- Move NTP servers from network/time.nix to hosts/default.nix
- Remove network/proxy.nix and network/smtp.nix (host-specific settings don't belong in network/)
- Update network/default.nix to only import dns.nix and time.nix

This refactoring separates environment-specific network parameters (domain, timezone)
from host-specific settings (DNS servers, SMTP, proxy, NTP servers), making the
configuration more logical and maintainable.

environments/sample/hosts/servers/dns01/configuration.nix

@@ -0,0 +1,26 @@
+{ config, pkgs, lib, ... }:
+
+{
+  imports = [
+    # Import the LXC machine type and DNS service from the framework
+    ../../../../modules/machine-types/lxc
+    ../../../../modules/services/dns/default.nix
+  ];
+
+  # Enable LXC machine type
+  lxc.enable = true;
+
+  # Host identity — replace with your own hostname and IP
+  networking.hostName = "dns01";
+  networking.useDHCP = true;
+
+  # DNS service configuration — adapt to your network
+  services.dns = {
+    enable = true;
+    recursion = "AllowOnlyForPrivateNetworks";
+    forwarders = [ "1.1.1.1" "8.8.8.8" ];
+    listenAddresses = [ "10.0.0.10" "127.0.0.1" "::1" ];
+  };
+
+  system.stateVersion = "25.11";
+}