Implement modular Plasma taskbar pinning system

- Add modular pinning system using NixOS module options
- Each desktop module now defines its own pinned applications:
  * plasma.nix: konsole, dolphin, firefox, tigervnc
  * gaming.nix: steam, discord
  * office.nix: slack, signal, libreoffice-writer, libreoffice-calc
  * dev.nix: windsurf
  * media.nix: rustdesk
  * dnm.nix: tor-browser, kleopatra (moved from crypto.nix)
- Move Plasma config from user-specific to desktop module for consistency
- Rename crypto.nix to dnm.nix and update references
- All users with Plasma desktop get automatic taskbar pinning
- Applications only appear when their desktop modules are active

flake.nix

@@ -47,7 +47,7 @@
         ./desktop/gaming.nix
         ./desktop/media.nix
         ./desktop/virtualization.nix
-        ./desktop/crypto.nix
+        ./desktop/dnm.nix
       ];
     in {
     nixosConfigurations = {