treewide: impermanence configuration

modules/nixos/services/tailscale.nix

@@ -56,5 +56,9 @@ in
       trustedInterfaces = [ "tailscale0" ];
       allowedUDPPorts = [ config.services.tailscale.port ];
     };
+
+    environment.persistence."/state".directories = [
+      "/var/lib/tailscale"
+    ];
   };
 }