Title bar button: fixes from trying it in the live desktop

- The decoration's "bottom" property clashed with Item's (KWin refused it).
- No On All Desktops button with one virtual desktop, like Breeze.
- decoration/apply.sh finds the session's D-Bus through plasmashell (KWin's
  environment isn't readable), and installs each try under a new name: KWin
  keeps a decoration's QML by name until it restarts.
- ft-floatd starts its script with Scripting.start: after a reload, the new
  script gets the old one's id while the old one is still being deleted, so
  run() on /Scripting/Script<id> went to the old script and the new one never
  ran (a second ft-floatd start left floating windows without their script).

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

float/ft_floatd.py

@@ -197,7 +197,10 @@ class Daemon:
         sid = int(kwin.loadScript(os.path.join(HERE, "frametop-float.js"), SCRIPT, signature="ss"))
         if sid < 0:
             raise RuntimeError("KWin didn't load the script")
-        bus.get_object("org.kde.KWin", f"/Scripting/Script{sid}").run(dbus_interface="org.kde.kwin.Script")
+        # Scripting.start runs every loaded script that isn't running. Not /Scripting/Script<id>'s
+        # run: a reloaded script gets the old one's id while the old one is still being deleted,
+        # so that path is still the old script's, and the new one would never run.
+        kwin.start()
         log(f"script loaded ({sid})")
         # Older scripts registered the float key with KWin; the input relay owns it now. Drop
         # that shortcut, so System Settings doesn't list one that does nothing.