Layouts, iPad-style rendering, taps, shift and layers

- JSON layouts (en-US, sv-SE inheriting number/symbol layers via base)
- LayoutModel + KeyGeometry: proportional rows, nearest-key hit testing
- KeyboardSurface: multi-pointer touch/mouse routing to the controller
- KeyboardController + ShiftState: iOS shift/caps-lock, layers, globe, dismiss
- QML view with light/dark iPad palette and drag handle
- DevHooks: SLOPOSK_AUTOTYPE, SLOPOSK_SCREENSHOT for headless checks
- Unit tests for shift, loader, geometry and controller

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

qml/DragHandle.qml

@@ -0,0 +1,30 @@
+import QtQuick
+
+// The grab bar under the floating keyboard. Emits how far it was dragged;
+// moving the window is up to the owner.
+Item {
+    id: handle
+
+    signal moved(real dx, real dy)
+
+    implicitHeight: 22
+
+    Rectangle {
+        anchors.centerIn: parent
+        width: 120
+        height: 5
+        radius: height / 2
+        color: Theme.handle
+    }
+
+    DragHandler {
+        target: null
+        // The window follows the pointer, so the pointer stays near its press
+        // position in window coordinates: measure each step from there.
+        onCentroidChanged: {
+            if (active)
+                handle.moved(centroid.scenePosition.x - centroid.scenePressPosition.x,
+                             centroid.scenePosition.y - centroid.scenePressPosition.y)
+        }
+    }
+}