fix(desktop): dark ssh-askpass pinentry via hyprland env

QT_QPA_PLATFORMTHEME=gtk3 (what makes Qt apps read Adwaita-dark) reaches
the systemd-user env — so gpg-agent's signing pinentry is dark — but not
Hyprland's children, so the shell-spawned ssh askpass pinentry launched
without it and came up light. Export it in the compositor env so every
session child inherits it. Keeps pinentry-qt.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home.nix

@@ -443,6 +443,15 @@ in
     settings = {
       monitor = ",preferred,auto,1";
 
+      # The qt module sets QT_QPA_PLATFORMTHEME=gtk3 (→ Qt apps read the GTK
+      # Adwaita-dark theme), but only into hm-session-vars.sh + the systemd user
+      # env. gpg-agent (a user service) inherits it, so commit-signing pinentry
+      # is dark — but Hyprland doesn't source that file, so its children (foot →
+      # shell → ssh askpass → pinentry) launch without it and came up light.
+      # Verified the single var flips pinentry-qt dark; export it here so every
+      # session child gets it too.
+      env = [ "QT_QPA_PLATFORMTHEME,gtk3" ];
+
       general = {
         layout = "master";
         gaps_in = 5;