migrate: Qt5/C++11 app to Qt6/C++23 with tests and modern Qt APIs

Entire-Checkpoint: c1ee98dc34a3

ci/Dockerfile.ci

@@ -21,4 +21,10 @@ RUN apt-get update && \
       qt6-tools-dev-tools && \
     rm -rf /var/lib/apt/lists/*
 
+# Set Qt platform for headless testing
+ENV QT_QPA_PLATFORM=offscreen
+
+# Configure git for containerized environments
+RUN git config --global --add safe.directory "*"
+
 WORKDIR /workspace