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>

docs/floating-windows.md

@@ -10,7 +10,7 @@ Built so far (2026-09-29; the KWin side tested on the headless test desktop, `sc
 - The session adds `FLOAT_SLOTS` spares and starts ft-floatd from the desktop's autostart; ft-layout leaves the spares alone.
 - The 3D mouse's drag lock crosses onto other Frametop panels (not while carrying one).
 - The float key (2026-09-30): the input relay's `float_toggle` (Meta+Shift+F by default) and `dock_all`, through `float pointer` and `dock all` on ft-floatd. Tested on the headless desktop.
-- The title bar button (2026-09-30, branch `float-titlebar`): `decoration/` (Frametop's QML window decoration, installed by the session script; `decoration/apply.sh` switches the running desktop to it or back to Breeze), and keep-below as the floating flag in the script. Not yet tried in a running KWin.
+- The title bar button (2026-09-30, branch `float-titlebar`): `decoration/` (Frametop's QML window decoration, installed by the session script; `decoration/apply.sh` switches the running desktop to it or back to Breeze), and keep-below as the floating flag in the script. Tried on the live desktop: the button floats Dolphin and docks it again, the float key and `dock all` keep the flag in step, and maximized windows look right.
 
 Not built yet: phase 2 (the ghost, tear-off by dragging, push-flush docking), phase 3 (launching floating, Launch as Standalone, remembered placement), and phase 4.