Polish BOS: dark theme, shell QoL, icons, media, clipboard

- Global dark theme: gnome-themes-extra (GTK3 Adwaita-dark), qt5ct/qt6ct
  with Fusion dark skel config, QT_QPA_PLATFORMTHEME=qt5ct env
- Icons/cursor: papirus-icon-theme (Papirus-Dark) + bibata-cursor-theme
  (Bibata-Modern-Ice), set via gsettings autostart + GTK settings.ini + env
- gnome-keyring: credential storage for browsers and apps
- gvfs + gvfs-mtp: nautilus trash, phone access, network shares
- zsh: default user shell (users.conf userShell=/bin/zsh) + skel .zshrc
  with eza/bat/fzf/zoxide aliases, git prompt, fzf history search
- Shell QoL packages: eza, bat, fzf, zoxide
- Media: gst-plugins-good/bad/ugly, pavucontrol
- cliphist: clipboard history daemon (autostart) + SUPER+SHIFT+V bind
- Fonts: noto-fonts-cjk, ttf-jetbrains-mono-nerd

iso/airootfs/etc/skel/.config/gtk-3.0/settings.ini

@@ -1,3 +1,7 @@
 [Settings]
 gtk-application-prefer-dark-theme=1
 gtk-theme-name=Adwaita-dark
+gtk-icon-theme-name=Papirus-Dark
+gtk-cursor-theme-name=Bibata-Modern-Ice
+gtk-cursor-theme-size=24
+gtk-font-name=Noto Sans 11