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>

src/engine/DirectEngine.cpp

@@ -0,0 +1,18 @@
+#include "DirectEngine.h"
+
+#include "backend/TextBackend.h"
+
+DirectEngine::DirectEngine(TextBackend &backend)
+    : m_backend(backend)
+{
+}
+
+void DirectEngine::commitText(const QString &text)
+{
+    m_backend.commitText(text);
+}
+
+void DirectEngine::sendKeysym(quint32 keysym)
+{
+    m_backend.sendKeysym(keysym);
+}