fix(emacs): start with graphical session

modules/home/emacs.nix

@@ -171,6 +171,14 @@ in {
         client.enable = true;
       };
 
+      # Start Emacs after the graphical session so as to inherit
+      # expected envvars, but don't necessarily /depend/ on a
+      # graphical session.
+      systemd.user.services.emacs = {
+        Unit.After = [ "graphical-session.target" ];
+        Install.WantedBy = lib.mkForce [ "graphical-session.target" ];
+      };
+
       # We do this ourselves.
       stylix.targets.emacs.enable = false;
     });