refactor: clean up Waybar styles, remove user-defaults mechanism

- Remove defaults/user/ and the user-defaults copy loop from
  post-install.sh and transform.sh — Waybar falls back to
  /etc/xdg/waybar/ via XDG spec, no provisioning needed.
- Remove USER_DEFAULTS constant from lib.sh.
- Clean up style.css: remove dead selectors (#net, #cava,
  #custom-updates, #custom-notification), commented-out blocks,
  empty rules, duplicate properties, and hardcoded hex color.
- Restructure module styling: generic top-level box via
  > widget > *, group children reset via widget widget > *,
  explicit exceptions for workspaces/taskbar/window.
- Normalize section comments and whitespace.
- Update README to remove user/waybar/ from project structure.

scripts/lib.sh

@@ -8,7 +8,6 @@ PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
 OFFICIAL_PACKAGES="$PROJECT_DIR/packages/official.txt"
 AUR_PACKAGES="$PROJECT_DIR/packages/aur.txt"
 DEFAULTS_DIR="$PROJECT_DIR/defaults"
-USER_DEFAULTS="/usr/share/moonarch/user-defaults"
 
 # --- Helper functions ---