Gui/initial gui

[vhrabar]

This pull request introduces a new Qt-based GUI application for SecureEye, along with supporting build system updates and environment variable overrides for configuration paths. The main themes are the addition of the GUI, build system enhancements for Qt dependencies, and improved configuration flexibility.

New GUI application:

• Added a new Qt6-based GUI application (secureeye-gui) with its own C++ entry point (src/main.cpp), application logic (src/app/Application.cpp, src/app/Application.hpp), QML user interface (qml/main.qml, qml/pages/Dashboard.qml), and resource file (secureeye-gui.qrc). The GUI includes a Kirigami-based dashboard and navigation drawer. [1] [2] [3] [4] [5] [6]
• Added desktop entry (secureeye-gui.desktop) and icon resources for integration with Linux desktop environments. [1] [2]

Build system and CI updates:

• Updated meson.build and meson.options to support building and installing the GUI, controlled by the new install_gui option (enabled by default). The GUI build is conditional and installs binaries, desktop files, and icons. [1] [2] [3]
• Updated GitHub Actions workflows (check.yml, CodeQL.yml, release-debs.yml) to install Qt6 and gettext dependencies required for the GUI build. [1] [2] [3]

Configuration and environment overrides:

• Enhanced paths_factory.py to allow overriding default configuration and data paths using environment variables, improving development and deployment flexibility. [1] [2]