fix(pm/tailscale): use client routing

We hadn't set up client routing on our personal machines, which stopped
us from using exit nodes/routes/etc.

packetmix/systems/common/tailscale.nix

···
 #
 # SPDX-License-Identifier: MIT
 {
-  services.tailscale.enable = true;
+  services.tailscale = {
+    enable = true;
+    useRoutingFeatures = "client";
+  };
 
   systemd.services.tailscaled.environment.TS_NO_LOGS_NO_SUPPORT = "true";
 

packetmix/systems/server/tailscale.nix

···
 #
 # SPDX-License-Identifier: MIT
 
+{ lib, ... }:
 {
-  services.tailscale.useRoutingFeatures = "both";
+  services.tailscale.useRoutingFeatures = lib.mkForce "both";
 }