Float as a KWin-managed window instead of a layer surface

The grab bar didn't move the window by mouse, and the corner grip never
resized it (the bar's handler took over its drag). The bar and grip now
start the window manager's move/resize, and Super+LMB/RMB work too.

A KWin rule in kwinrulesrc keeps the window above and unfocused, off the
taskbar, pager and switcher, and remembers its position. KWin now places
the window and keeps it on screen.

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

README.md

@@ -22,7 +22,7 @@ cmake -B build -G Ninja && cmake --build build
 ctest --test-dir build
 ```
 
-Needs Qt ≥ 6.8 (Quick, WaylandClient, DBus, Test), LayerShellQt, KF6 WindowSystem, xkbcommon, wayland-protocols.
+Needs Qt ≥ 6.8 (Quick, WaylandClient, DBus, Test), KF6 WindowSystem, KF6 Config, xkbcommon, wayland-protocols.
 
 ## Run
 
@@ -73,7 +73,7 @@ input/      touch → PointerTracker gestures → KeyboardController rules
 engine/     key output → text ops (DirectEngine; prediction/swipe later)
 backend/    text ops → compositor (KWin input-method-v1, or fake input with no text field); the compositor's keymap
 layout/     template JSON + keymap letters → Layout → LayoutModel (geometry, hit testing)
-window/     floating layer-shell placement, visibility, saved geometry
+window/     floating window (KWin rule: on top, no focus), visibility, saved geometry
 app/        D-Bus control and system layouts, dev hooks
 settings/   persisted user preferences
 ```