Gestures: flick, long-press alternates, trackpad, layer slide, rollover

- PointerTracker: per-finger gesture state machine (pure, unit-tested)
- AlternatesPicker + AlternatesPopup.qml: long-press choices, finger selects
- Space long-press trackpad moves the cursor with arrow keysyms
- Slide from .?123 onto a symbol types it and switches back
- New finger commits pending taps (iOS rollover)
- Flick animation: secondary symbol slides down as the finger moves
- Transparent popup margin with an input region that passes clicks through
- tst_keyboardsurface: end-to-end gesture tests on the real QML

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

tests/CMakeLists.txt

@@ -9,3 +9,10 @@ sloposk_add_test(tst_shiftstate)
 sloposk_add_test(tst_layoutloader)
 sloposk_add_test(tst_keygeometry)
 sloposk_add_test(tst_controller)
+sloposk_add_test(tst_pointertracker)
+sloposk_add_test(tst_alternatespicker)
+
+# Needs the QML module itself, not just the C++ backing library.
+sloposk_add_test(tst_keyboardsurface)
+target_link_libraries(tst_keyboardsurface PRIVATE sloposk_coreplugin)
+set_tests_properties(tst_keyboardsurface PROPERTIES ENVIRONMENT "QT_QPA_PLATFORM=offscreen;QT_QUICK_BACKEND=software")