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

desktop/dnm.nix

@@ -0,0 +1,16 @@
+{ config, pkgs, lib, ... }:
+
+{
+  # Add this module's pinned applications
+  desktop.plasma.pinnedApps = [
+    "applications:tor-browser.desktop"         # Tor browser
+    "applications:org.kde.kleopatra.desktop"   # Kleopatra GPG
+  ];
+
+  environment.systemPackages = with pkgs; [
+    feather
+    electrum
+    kdePackages.kleopatra
+    tor-browser
+  ];
+}