Reduce compiler warnings: replace qAsConst with std::as_const and update event localPos() to position()

Replaced deprecated qAsConst usages in built modules and updated QMouseEvent::localPos() to position() per Qt6 deprecation guidance.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/gtest/README.md

@@ -0,0 +1,11 @@
+Generated GoogleTest stubs for Z/src.
+
+Usage:
+  python3 tests/gtest/generate_gtests.py    # generate test sources and CMakeLists
+  cmake -S . -B build
+  cmake --build build -- -j5
+  ctest --test-dir build -j5
+
+Notes:
+- Tests are lightweight smoke stubs that compile and assert true. Replace with meaningful assertions per-function.
+- Uses FetchContent to download GoogleTest at configure time.