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/roles/profile_desktop_gnome/tasks/main.yml

@@ -1,59 +0,0 @@
----
-- name: Ensure GNOME desktop session is enabled for this profile
-  tags: [gnome]
-  ansible.builtin.assert:
-    that:
-      - "'gnome' in (desktop_sessions_enabled | default([]))"
-    fail_msg: >-
-      profile_desktop_gnome requires desktop_sessions_enabled to include gnome.
-
-- name: Ensure systemd boots to the graphical target
-  tags: [services, gnome]
-  ansible.builtin.file:
-    src: /usr/lib/systemd/system/graphical.target
-    dest: /etc/systemd/system/default.target
-    state: link
-    force: true
-    owner: root
-    group: root
-
-- name: Enable emacs user service from package
-  tags: [services, emacs]
-  ansible.builtin.systemd:
-    name: emacs.service
-    enabled: true
-    scope: user
-  become_user: "{{ username }}"
-
-- name: Deploy gpg-agent.conf for GNOME (pinentry-gnome3, no ssh-support)
-  tags: [dotfiles, dotfiles:desktop, gnome]
-  ansible.builtin.copy:
-    src: "{{ playbook_dir }}/../dotfiles/desktop/.gnupg/gpg-agent.arch.conf"
-    dest: "{{ user_home }}/.gnupg/gpg-agent.conf"
-    owner: "{{ username }}"
-    group: "{{ user_group }}"
-    mode: "0600"
-
-- name: Enable gnome-keyring PAM auth hook for GDM
-  tags: [gnome]
-  ansible.builtin.lineinfile:
-    path: /etc/pam.d/gdm-password
-    insertafter: '^auth\s+include\s+system-local-login$'
-    line: "auth       optional  pam_gnome_keyring.so"
-    state: present
-
-- name: Enable gnome-keyring PAM session hook for GDM
-  tags: [gnome]
-  ansible.builtin.lineinfile:
-    path: /etc/pam.d/gdm-password
-    insertafter: '^session\s+include\s+system-local-login$'
-    line: "session    optional  pam_gnome_keyring.so auto_start"
-    state: present
-
-- name: Enable gnome-keyring PAM password hook for GDM
-  tags: [gnome]
-  ansible.builtin.lineinfile:
-    path: /etc/pam.d/gdm-password
-    insertafter: '^password\s+include\s+system-local-login$'
-    line: "password   optional  pam_gnome_keyring.so use_authtok"
-    state: present