Remove Arch/nymph path, restore nymph as Void desktop

Delete all Arch-specific files (packages_arch role, profile_desktop_gnome
role, arch.yml group_vars, nymph.yml host_vars, arch dotfiles). Revert
nymph to the void group in inventory, remove the arch play from site.yml,
and restore profile_desktop_host/tasks/nymph.yml to its pre-Arch state
(GRUB + NVIDIA + prime-run). Preserve Void improvements introduced
alongside Arch work (desktop_void_dotfiles, desktop_void_source_tools,
profile_desktop_i3 dir additions, void-specific conditions).

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

ansible/inventory/group_vars/desktop.yml

@@ -112,20 +112,6 @@ desktop_common_dotfiles:
     dest: .ssh/config
     mode: "0600"
 
-desktop_arch_dotfiles:
-  - name: rclone pcloud systemd user service
-    src: .config/systemd/user/rclone-pcloud.service
-    dest: .config/systemd/user/rclone-pcloud.service
-    mode: "0644"
-  - name: syncthing systemd user service
-    src: .config/systemd/user/syncthing.service
-    dest: .config/systemd/user/syncthing.service
-    mode: "0644"
-  - name: MIME application defaults
-    src: .config/mimeapps.arch.list
-    dest: .config/mimeapps.list
-    mode: "0644"
-
 desktop_emacs_dotfiles:
   - name: Emacs config
     src: .emacs.d/