Fix dunst config loading, modernize notification handling

- Point dunst to /etc/xdg/dunst/dunstrc via -conf flag (dunst with
  SYSCONFDIR=/etc does not search XDG_CONFIG_DIRS)
- Update dunstrc: fix legacy offset syntax, replace missing
  Tela-purple-dark icon theme with Colloid-Grey-Catppuccin-Dark
- Replace dunstify with notify-send in moonarch-cpugov for
  daemon-agnostic notifications, fix broken icon path
- Replace dbus-monitor based moonarch-dnd script with inline
  waybar polling (interval 2s), fixing process accumulation bug
- Add #custom-dnd to waybar CSS padding rule

defaults/xdg/dunst/dunstrc

@@ -38,7 +38,7 @@
     origin = top-right
 
     # Offset from the origin
-    offset = 15x15
+    offset = (15, 15)
 
     # Scale factor. It is auto-detected if value is 0.
     scale = 0
@@ -202,7 +202,7 @@
     enable_recursive_icon_lookup = true
 
     # Set icon theme (only used for recursive icon lookup)
-    icon_theme = "Tela-purple-dark"
+    icon_theme = "Colloid-Grey-Catppuccin-Dark"
     # You can also set multiple icon themes, with the leftmost one being used first.
     # icon_theme = "Adwaita, breeze"