refactor: rename some flake attr directories

modules/server/default.nix

@@ -0,0 +1,30 @@
+{lib, ...}: let
+  inherit (lib) mkOption types;
+in {
+  imports = [
+    ./sshd.nix
+    ./tailscale.nix
+  ];
+
+  options.roles.server = {
+    user = mkOption {
+      type = types.str;
+      description = ''
+        The name of the machine's main user.
+      '';
+    };
+
+    sshd.enable = mkOption {
+      type = types.bool;
+      default = false;
+    };
+
+    tailscale.enable = mkOption {
+      type = types.bool;
+      default = false;
+    };
+  };
+
+  # For accurate stack trace
+  _file = ./default.nix;
+}