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>

tests/CMakeLists.txt

@@ -0,0 +1,11 @@
+function(sloposk_add_test name)
+    qt_add_executable(${name} ${name}.cpp)
+    target_link_libraries(${name} PRIVATE sloposk_core Qt6::Test)
+    add_test(NAME ${name} COMMAND ${name})
+    set_tests_properties(${name} PROPERTIES ENVIRONMENT "QT_QPA_PLATFORM=offscreen")
+endfunction()
+
+sloposk_add_test(tst_shiftstate)
+sloposk_add_test(tst_layoutloader)
+sloposk_add_test(tst_keygeometry)
+sloposk_add_test(tst_controller)