Inline one-liner system modules into host defaults

- services.openssh.enable, virtualisation.docker.enable into hivebrain
- services.displayManager.sddm.enable, services.desktopManager.plasma6.enable into nikita-nixos
- Remove four no-longer-needed system modules

hosts/hivebrain/default.nix

@@ -10,10 +10,8 @@
     ../../system/locale.nix
     ../../system/fonts.nix
     ../../system/nix.nix
-    ../../system/ssh.nix
     ../../system/programs.nix
     ../../system/packages.nix
-    ../../system/docker.nix
 
     # marvin-only
     ../../system/xserver.nix
@@ -26,5 +24,8 @@
   networking.hostName = "hivebrain";
   system.stateVersion = "26.05";
 
+  services.openssh.enable = true;
+  virtualisation.docker.enable = true;
+
   programs.steam.enable = true;
 }

hosts/nikita-nixos/default.nix

@@ -14,11 +14,12 @@
     ../../system/packages.nix
 
     # nikita-only
-    ../../system/plasma.nix
-    ../../system/display-managers/sddm.nix
     ../../system/users/nikita.nix
   ];
 
   networking.hostName = "nikita-nixos";
   system.stateVersion = "26.05";
+
+  services.displayManager.sddm.enable = true;
+  services.desktopManager.plasma6.enable = true;
 }