A float button in every window's title bar

Frametop's own window decoration (decoration/), a QML decoration for KWin's
Aurorae engine drawn like Breeze, puts a float button left of Close. It's the
Keep Below button with its own glyph: the KWin script floats a window when
keep-below is set and docks it when it's cleared, and keeps the flag set on
every floating window, so the button shows "back to the desktop" there. The
session script installs the decoration for the Frametop desktop only;
decoration/apply.sh switches a running desktop to it or back to Breeze.

Not yet tried in a running KWin.

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

float/ft_floatd.py

@@ -355,6 +355,7 @@ class Daemon:
             return
         slot = self.free_slot()
         if slot is None:
+            self.command(cmd="mark", id=wid)  # the title bar button set keep-below for nothing
             self.notify(f"All {len(self.slots)} floating windows are in use. Put one back on the desktop "
                         "to float another.")
             return