Fix GoofCord desktop matching with lowercase StartupWMClass

Electron sets the Wayland app_id from the package name (lowercase
"goofcord") but the desktop file had StartupWMClass=GoofCord
(capitalized), causing GNOME to not match the window to its icon.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hosts/FredOS-Gaming.nix

@@ -14,6 +14,8 @@
         postFixup = (old.postFixup or "") + ''
           substituteInPlace $out/bin/goofcord \
             --replace-fail 'exec -a "$0"' 'NIXOS_OZONE_WL=1 exec -a "$0"'
+          substituteInPlace $out/share/applications/goofcord.desktop \
+            --replace-fail 'StartupWMClass=GoofCord' 'StartupWMClass=goofcord'
         '';
       }))
       lsfg-vk