Add ft-floatd and the frametop-float KWin script

ft-floatd loads the script into the desktop's KWin, which reports windows
over D-Bus and takes commands through a long poll. Floating a window (the
window menu's Float in VR, Meta+Shift+F, or ft-float) turns on a spare
output sized to the window plus a margin, moves the window onto it, and
tells ft-screens the panel's crop, density, and place; docking puts it
back and turns the spare off. Tested on the headless test desktop; the
panel side in ft-screens comes next.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

float/ft-floatd

@@ -0,0 +1,3 @@
+#!/bin/bash
+# ft-floatd on the Frame host, inside the Frametop desktop's session (see ft_floatd.py).
+exec python3 "$(dirname "$(readlink -f "$0")")/ft_floatd.py" "$@"