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>

qml/Main.qml

@@ -17,6 +17,8 @@ Window {
 
     width: 1000
     height: 340 + popupMargin
+    minimumWidth: 480
+    minimumHeight: 180 + popupMargin
     visible: false
     color: "transparent"
 
@@ -42,5 +44,10 @@ Window {
             anchors { left: parent.left; right: parent.right; bottom: parent.bottom }
             onMoved: (dx, dy) => root.placement?.moveBy(dx, dy)
         }
+
+        ResizeHandle {
+            anchors { right: parent.right; bottom: parent.bottom }
+            onResized: (dw, dh) => root.placement?.resizeBy(dw, dh)
+        }
     }
 }