add aspects/hosts/ configurations

Host-specific NixOS configurations for:
- alexandria (server)
- io (desktop)
- rotterdam (desktop)
- trantor (server, aarch64)

Each host has a main config file and _hostname/ directory
with hardware-configuration and other host-specific modules.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

aspects/hosts/_alexandria/unbound.nix

@@ -0,0 +1,58 @@
+{ inputs, lib, ... }:
+
+let
+  utils = import ../../../utils.nix { inherit inputs lib; };
+in
+
+{
+  services.unbound = {
+    enable = true;
+    enableRootTrustAnchor = true;
+    settings = {
+      server = {
+        interface = [
+          "0.0.0.0"
+          "::"
+        ];
+        access-control = [
+          "127.0.0.0/8 allow"
+          "192.168.0.0/16 allow"
+          "::1/128 allow"
+        ];
+
+        num-threads = 2;
+        msg-cache-size = "50m";
+        rrset-cache-size = "100m";
+        cache-min-ttl = 300;
+        cache-max-ttl = 86400;
+        prefetch = true;
+        prefetch-key = true;
+        hide-identity = true;
+        hide-version = true;
+        so-rcvbuf = "1m";
+        so-sndbuf = "1m";
+
+        # LAN-only DNS records
+        local-zone = ''"baduhai.dev." transparent'';
+        local-data = map (e: ''"${e.domain}. IN A ${e.lanIP}"'')
+          (lib.filter (e: e ? lanIP) utils.services);
+      };
+
+      forward-zone = [
+        {
+          name = ".";
+          forward-addr = [
+            "1.1.1.1@853#cloudflare-dns.com"
+            "1.0.0.1@853#cloudflare-dns.com"
+          ];
+          forward-tls-upstream = true;
+        }
+      ];
+    };
+  };
+
+  networking.firewall = {
+    allowedTCPPorts = [ 53 ];
+    allowedUDPPorts = [ 53 ];
+  };
+}