Floating polish: visibility, resize, saved geometry, D-Bus, desktop entry

- VisibilityController: show on field focus, dismiss until next focus,
  manual show/hide/toggle overrides
- FloatingWindow: resize from the corner grip, clamp to screen
- WindowSettings: geometry per screen, debounced saves
- DBusControl: org.sloposk.Keyboard Show/Hide/Toggle for global shortcuts
- org.sloposk.keyboard.desktop so System Settings lists it as a virtual keyboard
- README with build/run/layout docs

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

CMakeLists.txt

@@ -5,7 +5,7 @@ set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
-find_package(Qt6 6.8 REQUIRED COMPONENTS Gui Quick Widgets Test WaylandClient)
+find_package(Qt6 6.8 REQUIRED COMPONENTS Gui Quick Widgets Test DBus WaylandClient)
 find_package(LayerShellQt REQUIRED)
 find_package(PkgConfig REQUIRED)
 pkg_check_modules(XKB REQUIRED IMPORTED_TARGET xkbcommon)
@@ -13,6 +13,7 @@ pkg_check_modules(WAYLAND REQUIRED IMPORTED_TARGET wayland-client)
 pkg_get_variable(WAYLAND_PROTOCOLS_DIR wayland-protocols pkgdatadir)
 
 qt_standard_project_setup(REQUIRES 6.8)
+include(GNUInstallDirs)
 
 enable_testing()