Show floating windows as panels of their own

ft-screens makes a panel for each spare output (frametop.float.N), hidden
until ft-floatd floats a window on it. The panel shows only the window's
rectangle of the buffer at the density of the screen it came from, its
popups and dialogs get small panels over it, pressing its title bar
carries it while KWin's pointer stays put, the corner tab resizes the
window in pixels, and two more buttons close it and put it back on the
desktop. The session adds FLOAT_SLOTS spare outputs to KWin and starts
ft-floatd; ft-layout arranges only the screens' outputs, and the pointer
helper treats the new panels like screens. Not yet tried in the headset.

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

float/ft_floatd.py

@@ -305,6 +305,7 @@ class Daemon:
         # The spare's size first (while it's off, so its first frame is right), then its panel,
         # then turn it on, then the window.
         self.screens.ask(f"size {slot.index} {slot.size[0]} {slot.size[1]}")
+        self.screens.ask(f"scale {slot.index} {s:g}")  # for pointer positions (KWin's units)
         self.set_panel(f, (m, m, w, h), title=round((ev["client"]["y"] - fr["y"]) * s))
         self.place_panel(f, ev)
         kscreen(f"output.{slot.output}.enable", f"output.{slot.output}.scale.{s:g}",