feat(direnv): set up direnv using '.envrc'

.envrc

@@ -0,0 +1 @@
+use flake

hosts/eetion/default.nix

@@ -9,9 +9,12 @@
     ./host.nix
     ../../modules/common
     ../../modules/ssh
+    ../../modules/tailscale
     # ../../modules/uptime-kuma
   ];
 
+  tailscale.enable = true;
+
   ssh = {
     inherit (config.host) username;
     publicHostname = config.host.name;