Phase 3: screenshot hotkeys, clipboard history, Papirus icon theme

Screenshots (PrintScreen / Shift+PrintScreen):
- PrintScreen → full screenshot saved to ~/Pictures via scrot
- Shift+PrintScreen → interactive region select via scrot -s
- Both send a dunst notification on save
- scrot added to packages

Clipboard manager:
- Replace janky PRIMARY/CLIPBOARD sync loop with parcellite
- parcellite provides clipboard history, survives app close,
  shows a tray icon for browsing past entries
- parcellite added to packages

Icon theme:
- Switch from Adwaita to Papirus-Dark across GTK2, GTK3 settings,
  and theme index.theme
- papirus-icon-theme added to packages

Also fix remaining stale sky* references in menu.c (skywallpaper,
pkill skywm) and events.c (skylauncher).

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

themes/OrionOS/gtk-2.0/gtkrc

@@ -64,7 +64,7 @@ style "entry" {
 class "GtkEntry" style "entry"
 
 gtk-theme-name        = "OrionOS"
-gtk-icon-theme-name   = "Adwaita"
+gtk-icon-theme-name   = "Papirus-Dark"
 gtk-font-name         = "Sans 10"
 gtk-cursor-theme-name = "DMZ-White"
 gtk-button-images     = 0

themes/OrionOS/index.theme

@@ -7,6 +7,6 @@ Encoding=UTF-8
 [X-GNOME-Metatheme]
 GtkTheme=OrionOS
 MetacityTheme=OrionOS
-IconTheme=Adwaita
+IconTheme=Papirus-Dark
 CursorTheme=DMZ-White
 ButtonLayout=close:minimize,maximize