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/calamares/modules/users.conf

@@ -38,3 +38,4 @@ passwordRequirements:
     - minlen=6
 
 allowWeakPasswords: false
+userShell: /bin/zsh