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/default.nix

@@ -1,14 +1,27 @@
 { config, pkgs, lib, ... }:
 
-{
+let
+  # Import environment-specific network parameters
+  env = import ../../network { };
+in {
   # Common settings for all hosts in the sample environment
   # This file is imported by all host configurations (servers and workstations)
 
-  # TODO: Move common settings here later
+  # NTP servers for this environment
+  services.ntp.servers = [
+    "10.10.128.1"    # IPv4 gateway
+    "fd00::1"        # IPv6 gateway
+  ];
+
+  # Time settings from network configuration
+  time.timeZone = env.time.timeZone;
+  time.hardwareClock = env.time.hardwareClock;
+
+  # TODO: Move other common settings here later
   # Examples:
   # - Common users/groups
   # - Common packages
   # - Common services
   # - Common security policies
   # - Common monitoring/alerting
-}
+}