Add movie mode for watching videos on the external monitor

The screen layout and trayer setup moved from xmonad.hs to a shared
screen-layout script. lf opens videos with movie.

.local/bin/movie

@@ -0,0 +1,14 @@
+#!/bin/bash
+# Plays videos on the external monitor only, with the laptop screen off.
+# Opened from lf for video/* files; restores the normal layout when mpv exits.
+
+# Single-screen mode only makes sense with the external monitor plugged in
+if ! xrandr --query | grep -q '^HDMI-1-0 connected'; then
+    exec mpv "$@"
+fi
+
+trap ~/.local/bin/screen-layout EXIT
+trap 'exit 130' INT TERM HUP
+
+xrandr --output eDP-1 --off
+mpv "$@"