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

@@ -1,10 +1,23 @@
 { 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

environments/sample/hosts/servers/default.nix

@@ -1,10 +1,28 @@
 { config, pkgs, lib, ... }:
 
-{
+let
+  # Import environment-specific network parameters
+  env = import ../../../network { };
+in {
   # Common settings for all servers in the sample environment
   # This file is imported by all server configurations
 
-  # TODO: Move common server settings here later
+  # Default DNS servers for this environment
+  networking.nameServers = [ "10.40.128.10" ];
+
+  # SMTP relay configuration
+  services.postfix = {
+    enable = true;
+    relayHost = "smtp.lagraula.fr";
+    relayPort = 587;
+    useTLS = true;
+    fromAddress = "noreply@sample.lagraula.fr";
+  };
+
+  # Proxy configuration for servers (none for now)
+  environment.systemPackages = with pkgs; [ ];
+
+  # TODO: Move other common server settings here later
   # Examples:
   # - Server-specific users/groups
   # - Server-specific packages

environments/sample/hosts/workstations/default.nix

@@ -1,15 +1,35 @@
 { config, pkgs, lib, ... }:
 
-{
+let
+  # Import environment-specific network parameters
+  env = import ../../../network { };
+in {
   # Common settings for all workstations in the sample environment
   # This file is imported by all workstation configurations
 
-  # TODO: Move common workstation settings here later
+  # Default DNS servers for this environment
+  networking.nameServers = [ "10.40.128.10" ];
+
+  # SMTP relay configuration
+  services.postfix = {
+    enable = true;
+    relayHost = "smtp.lagraula.fr";
+    relayPort = 587;
+    useTLS = true;
+    fromAddress = "noreply@sample.lagraula.fr";
+  };
+
+  # Proxy configuration for workstations (none for now)
+  environment.systemPackages = with pkgs; [ ];
+
+  # Locale for workstations (French)
+  i18n.defaultLocale = "fr_FR.UTF-8";
+
+  # TODO: Move other common workstation settings here later
   # Examples:
   # - Workstation-specific users/groups
   # - Workstation-specific packages
   # - Workstation-specific services
   # - Workstation-specific security policies
   # - Workstation-specific monitoring/alerting
-  # - Locale: fr_FR.UTF-8 (for workstations)
 }

environments/sample/network/default.nix

@@ -11,6 +11,4 @@
 {
   dns = import ./dns.nix;
   time = import ./time.nix;
-  proxy = import ./proxy.nix;
-  smtp = import ./smtp.nix;
 }

environments/sample/network/dns.nix

@@ -4,9 +4,6 @@
   # Sample DNS configuration for the sample environment
   domain = "sample.lagraula.fr";
 
-  # Default DNS servers for this environment
-  defaultNameServers = [ "10.40.128.10" ];
-
   # Forwarders for this environment
   forwarders = [ "1.1.1.1" "8.8.8.8" ];
 
@@ -15,7 +12,4 @@
 
   # Recursion policy
   recursion = "AllowOnlyForPrivateNetworks";
-
-  # Email for Let's Encrypt
-  letsEncryptEmail = "xavier@lagraula.fr";
 }

environments/sample/network/proxy.nix

@@ -1,18 +0,0 @@
-{ config, pkgs, lib, ... }:
-
-{
-  # Proxy configuration for this environment
-  # Currently no proxy is used — direct access for all hosts
-
-  workstations = {
-    httpProxy = "";
-    httpsProxy = "";
-    noProxy = "";
-  };
-
-  servers = {
-    httpProxy = "";
-    httpsProxy = "";
-    noProxy = "";
-  };
-}

environments/sample/network/smtp.nix

@@ -1,12 +0,0 @@
-{ config, pkgs, lib, ... }:
-
-{
-  # SMTP relay configuration for this environment
-  relayHost = "smtp.lagraula.fr";
-  relayPort = 587;
-
-  useTLS = true;
-  useSTARTTLS = true;
-
-  fromAddress = "noreply@sample.lagraula.fr";
-}

environments/sample/network/time.nix

@@ -1,13 +1,7 @@
 { config, pkgs, lib, ... }:
 
 {
-  # NTP servers for this environment
+  # Time zone for this environment
-  ntpServers = [
-    "10.10.128.1"    # IPv4 gateway
-    "fd00::1"        # IPv6 gateway
-  ];
-
-  # Time zone
   timeZone = "Europe/Paris";
 
   # Hardware clock setting