feat(vps): enable IP forwarding for exit node support

Required so the host can route traffic as a Tailscale/Headscale exit node.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

hosts/vps/default.nix

@@ -71,6 +71,12 @@
   boot.loader.systemd-boot.configurationLimit = 10;
   boot.loader.efi.canTouchEfiVariables = true;
 
+  # Required for this host to act as a Tailscale/Headscale exit node.
+  boot.kernel.sysctl = {
+    "net.ipv4.ip_forward" = 1;
+    "net.ipv6.conf.all.forwarding" = 1;
+  };
+
   time.timeZone = "America/Argentina/Buenos_Aires";
   i18n.defaultLocale = "en_US.UTF-8";