feat: update sample environment to match nixos-infra structure

- Add network/dns.nix, network/time.nix, network/proxy.nix, network/smtp.nix
- Add network/default.nix to import all network files
- Add hosts/default.nix, hosts/servers/default.nix, hosts/workstations/default.nix
- These placeholders match the structure in nixos-infra for consistency

The sample environment now reflects the same organization as production,
dev, and stage environments, making it easier to use as a reference.

environments/sample/network/default.nix

@@ -0,0 +1,16 @@
+# Central network data source for the sample environment.
+#
+# Usage from a configuration.nix:
+#   network = import ../../network { };
+#   network.dns.domain  → "sample.lagraula.fr"
+#   network.time.timeZone → "Europe/Paris"
+#
+# Usage from a shell script (via `nix eval`):
+#   nix eval --json -f network/default.nix dns
+
+{
+  dns = import ./dns.nix;
+  time = import ./time.nix;
+  proxy = import ./proxy.nix;
+  smtp = import ./smtp.nix;
+}

environments/sample/network/dns.nix

@@ -0,0 +1,21 @@
+{ config, pkgs, lib, ... }:
+
+{
+  # 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" ];
+
+  # Allow zone transfers (none in sample)
+  allowZoneTransfer = [ ];
+
+  # Recursion policy
+  recursion = "AllowOnlyForPrivateNetworks";
+
+  # Email for Let's Encrypt
+  letsEncryptEmail = "xavier@lagraula.fr";
+}

environments/sample/network/proxy.nix

@@ -0,0 +1,18 @@
+{ 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

@@ -0,0 +1,12 @@
+{ 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

@@ -0,0 +1,15 @@
+{ config, pkgs, lib, ... }:
+
+{
+  # NTP servers for this environment
+  ntpServers = [
+    "10.10.128.1"    # IPv4 gateway
+    "fd00::1"        # IPv6 gateway
+  ];
+
+  # Time zone
+  timeZone = "Europe/Paris";
+
+  # Hardware clock setting
+  hardwareClock = "UTC";
+}