backwards: Add tailscale module

hosts/backwards/modules/tailscale/default.nix

@@ -0,0 +1,9 @@
+{ ... }:
+{
+  services.tailscale.enable = true;
+
+  networking.firewall = {
+    checkReversePath = "loose";
+    allowedUDPPorts = [ 41641 ];
+  };
+}