Clean up Arch profile: remove i3/Void-specific config and fix GNOME integration

- Remove XFCE/i3-specific packages and dotfiles from Arch path (xarchiver,
  udiskie, Thunar, xfce-polkit, clipman, screenshooter)
- Separate per-OS dotfiles: mimeapps, udiskie config, GTK theme script,
  udiskie-password, dbus-session and ssh-agent fragments moved to Void-only
- Add mimeapps.arch.list with Nautilus/GNOME associations for nymph
- Move dunst/rofi directory creation from common to profile_desktop_i3
- Add gnome-keyring PAM hooks for GDM (gdm-password) in profile_desktop_gnome
- Remove ssh-agent.service from desktop_systemd_user_services on Arch;
  drop ssh-agent dependency and hardcoded socket from emacs.service
- Add ttf-hack-nerd to Arch font packages
- Fix rustup bootstrap: use rustup-init on Void, rustup toolchain install on Arch

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

ansible/roles/profile_desktop_i3/tasks/main.yml

@@ -8,8 +8,10 @@
     group: "{{ user_group }}"
     mode: "0755"
   loop:
+    - "{{ user_home }}/.config/dunst"
     - "{{ user_home }}/.config/i3"
     - "{{ user_home }}/.config/i3blocks"
+    - "{{ user_home }}/.config/rofi"
   when: "'i3' in (desktop_sessions_enabled | default([]))"
 
 - name: Install allowed emptty X11 sessions