Add tailscale SSH host and use username variable

- Simplify server aliases and add tailscale‑specific aliases
- Make SSH module accept a username argument
- Add match block for Tailscale host with port 22 and identity file

modules/home/ssh.nix

@@ -1,11 +1,17 @@
-_: {
+{username, ...}: {
   programs.ssh = {
     enable = true;
     enableDefaultConfig = false;
     matchBlocks = {
       "hp-t640-homeserver" = {
         hostname = "192.168.1.156";
-        user = "garand_plg";
+        user = "${username}";
+        port = 22;
+        identityFile = "~/.ssh/hp-t640-homeserver";
+      };
+      "hp-t640-homeserver-tailscale" = {
+        hostname = "100.106.225.106";
+        user = "${username}";
         port = 22;
         identityFile = "~/.ssh/hp-t640-homeserver";
       };