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>

session/frametop-session.sh

@@ -204,7 +204,7 @@ deco=kwin4_decoration_qml_frametop
 deco_dir=${XDG_DATA_HOME:-$HOME/.local/share}/kwin/decorations/$deco
 kwinrc=$XDG_CONFIG_HOME/kwinrc
 if [ "$float_slots" -gt 0 ]; then
-  rm -rf "$deco_dir"
+  rm -rf "$deco_dir" "$deco_dir"_try*  # (decoration/apply.sh's copies)
   mkdir -p "$(dirname "$deco_dir")"
   cp -r "$here/../decoration" "$deco_dir"
   rm -f "$deco_dir/apply.sh"