Fix desktop file format in all desktop modules

- Remove incorrect 'applications:' prefix from desktop file names
- All modules now use correct format (e.g., 'steam.desktop' not 'applications:steam.desktop')
- Fixed modules: gaming.nix, office.nix, dev.nix, media.nix, dnm.nix
- Modular Plasma pinning system now works correctly for all desktop modules
- All 14 applications should now appear pinned after Plasma session restart

desktop/dev.nix

@@ -3,7 +3,7 @@
 {
   # Add this module's pinned applications
   desktop.plasma.pinnedApps = [
-    "applications:windsurf.desktop"     # Windsurf IDE
+    "windsurf.desktop"     # Windsurf IDE
   ];
 
   environment.systemPackages = with pkgs; [