Switch from clipit/gpaste to greenclip for clipboard management

- Remove clipit config and helper scripts
- Add greenclip service and rofi integration
- Update xmonad keybinding to use rofi_clipboard.sh

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nixos/home-manager.nix

@@ -1,5 +1,18 @@
 { pkgs, ... }:
 {
+  xdg.configFile."greenclip.toml".text = ''
+    [greenclip]
+      history_file = "~/.cache/greenclip.history"
+      max_history_length = 50
+      max_selection_size_bytes = 0
+      trim_space_from_selection = true
+      use_primary_selection_as_input = false
+      blacklisted_applications = []
+      enable_image_support = true
+      image_cache_directory = "~/.cache/greenclip"
+      static_history = []
+  '';
+
   xsession = {
     enable = true;
     preferStatusNotifierItems = true;