Add Ghostty, GNOME Tweaks, and a GNOME dark-mode default

Ghostty joins the cross-platform desktop app list (Linux-only in nixpkgs
today, filtered out on darwin by the existing availableOn check).
GNOME Tweaks is gated on osConfig.services.desktopManager.gnome.enable
rather than plain isLinux, since modules/home/desktop-apps.nix is also
consumed by the standalone, non-NixOS tom@linux home-manager profile,
which has no GNOME involved. Every NixOS host now also gets a dconf
default of org/gnome/desktop/interface color-scheme=prefer-dark, left
unlocked so GNOME Settings can still switch back to light mode.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HngxrvqEzq8oBEBDtrYJyB

2 files changed, 35 insertions, 6 deletions

diff --git a/modules/home/desktop-apps.nix b/modules/home/desktop-apps.nix
index 882ce34..a565c18 100644
--- a/modules/home/desktop-apps.nix
+++ b/modules/home/desktop-apps.nix
@@ -1,10 +1,28 @@
-{ pkgs, lib, ... }:
+{
+  pkgs,
+  lib,
+  osConfig ? null,
+  ...
+}:
 let
-  crossPlatformApps = [ pkgs.slack pkgs.discord pkgs.spotify pkgs.firefox pkgs.bitwarden-desktop ];
+  crossPlatformApps = [
+    pkgs.slack
+    pkgs.discord
+    pkgs.spotify
+    pkgs.firefox
+    pkgs.bitwarden-desktop
+    pkgs.ghostty
+  ];
   linuxOnlyApps = lib.optional pkgs.stdenv.hostPlatform.isLinux pkgs.teams-for-linux;
-  candidateApps = crossPlatformApps ++ linuxOnlyApps;
+  # GNOME Tweaks only makes sense where GNOME is actually enabled, which this
+  # flake only does at the NixOS level (modules/nixos/common.nix) - not on
+  # standalone, non-NixOS activations of this shared profile. osConfig is the
+  # full NixOS config and is only present when home-manager is integrated
+  # into a NixOS system; it's absent for standalone `home-manager switch`.
+  gnomeOnlyApps = lib.optional (osConfig.services.desktopManager.gnome.enable or false
+  ) pkgs.gnome-tweaks;
+  candidateApps = crossPlatformApps ++ linuxOnlyApps ++ gnomeOnlyApps;
 in
 {
-  home.packages =
-    builtins.filter (lib.meta.availableOn pkgs.stdenv.hostPlatform) candidateApps;
+  home.packages = builtins.filter (lib.meta.availableOn pkgs.stdenv.hostPlatform) candidateApps;
 }
diff --git a/modules/nixos/common.nix b/modules/nixos/common.nix
index 1b34e4e..a219850 100644
--- a/modules/nixos/common.nix
+++ b/modules/nixos/common.nix
@@ -1,6 +1,9 @@
 { pkgs, lib, ... }:
 {
-  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ];
 
   nix.gc = {
     automatic = true;
@@ -43,6 +46,14 @@
   services.displayManager.gdm.enable = true;
   services.desktopManager.gnome.enable = true;
 
+  # Defaults GNOME to dark mode without locking it - GNOME Settings'
+  # Appearance toggle still writes to the user's own dconf database, which
+  # is searched before this default database.
+  programs.dconf.enable = true;
+  programs.dconf.profiles.user.databases = [
+    { settings."org/gnome/desktop/interface".color-scheme = "prefer-dark"; }
+  ];
+
   networking.networkmanager.enable = true;
 
   services.pipewire = {