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/input/ShiftState.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <QtGlobal>
+#include <limits>
+
+// iOS shift semantics:
+//  - tap: shift the next character only
+//  - double-tap: caps lock; tap again to unlock
+//  - hold while typing: every character shifted, off on release
+// Times are in milliseconds and passed in, so this stays deterministic.
+class ShiftState
+{
+public:
+    enum class Mode { Off, Once, Locked };
+
+    static constexpr qint64 DoubleTapMs = 300;
+
+    Mode mode() const { return m_mode; }
+    bool isUppercase() const { return m_mode != Mode::Off; }
+
+    void press(qint64 timeMs);
+    void release();
+    void characterTyped();
+
+    // Auto-capitalization hint; ignored while shift is held or locked.
+    void setAutomatic(bool capitalize);
+
+private:
+    Mode m_mode = Mode::Off;
+    bool m_held = false;
+    bool m_typedWhileHeld = false;
+    qint64 m_lastPress = std::numeric_limits<qint64>::min() / 2;
+};