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/Keyboard.qml

@@ -0,0 +1,13 @@
+import QtQuick
+import Sloposk
+
+KeyboardSurface {
+    id: surface
+
+    Repeater {
+        model: surface.model
+        delegate: Key {
+            shiftMode: surface.controller ? surface.controller.shiftMode : KeyboardController.Off
+        }
+    }
+}