Shrink to a floating button instead of hiding

With "Shrink to Button" on, the dismiss key shrinks the window to just
itself: a see-through button that can be dragged anywhere. Tapping it
grows the keyboard back around it, kept on screen. KWin moves and
resizes the window through a one-off script, as Wayland clients can't
place themselves.

Also moves the window back on screen whenever it appears (KWin remembers
where the button was), and releases the mouse after a window manager
move or resize, which used to eat the next press on the grab bar.

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

README.md

@@ -14,6 +14,7 @@ iPad-style floating on-screen keyboard for Plasma Wayland. Qt 6, C++ core, QML U
 - Alt Gr (right of space in full mode) types the keymap's AltGr symbols (sk: Alt Gr+J = '), sticky like the others
 - Optional PC key blocks: function row, navigation (ins/home/pg up, del/end/pg dn, arrows), numeric keypad; any mix, typing keys included (⚙)
 - Floating: drag the bottom bar, resize from the corner; geometry is remembered per screen
+- "Shrink to Button" (⚙): ⌨ leaves just itself as a see-through floating button (drag it anywhere); tap it for the keyboard back, around the button and kept on screen
 - Follows Plasma's virtual keyboard setting (tray toggle): off never pops up on focus, the default only after touch or a pen; "Always Show" and D-Bus `Show`/`Toggle` still show it
 - See-through background (opacity slider in ⚙) with optional blur behind it (KWin's blur effect)