chore: drop redundant packages and options

- packages.nix is the baseline: drop neovim (nixvim), nvd, sof-firmware (enableAllFirmware), qtmultimedia (v4 leftover); vial moves to vial.nix, wl-clipboard to noctalia.nix, claude-code becomes a plain package here
- drop packages and options already provided elsewhere: noctalia (home-manager), gnupg/pinentry-qt (agent), gtk/qt themes, sddm Theme.Current, zsh plugins (home-manager), group = users, empty firewall lists
- single-package lists without `with pkgs;`, steam package inside its block

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

modules/nixos/sddm.nix

@@ -1,25 +1,15 @@
 { pkgs, ... }:
 
 {
-  # enable sddm and use astronaut theme
   services.displayManager.sddm = {
     enable = true;
     wayland.enable = true;
     autoNumlock = true;
     enableHidpi = true;
     theme = "sddm-astronaut-theme";
-    settings = {
-      Theme = {
-        Current = "sddm-astronaut-theme";
-      };
-    };
-    extraPackages = with pkgs; [
-      sddm-astronaut
-    ];
+    extraPackages = [ pkgs.sddm-astronaut ]; # theme's qml dependencies
   };
 
-  # Make the theme available in the system path so sddm can find it
-  environment.systemPackages = with pkgs; [
-    sddm-astronaut
-  ];
+  # sddm looks for themes in the system path
+  environment.systemPackages = [ pkgs.sddm-astronaut ];
 }