1.4.0

This is a minor upgrade with new features, build-system modernization, and bug fixes.

Added a new `Global.py` metadata system so version, release date, build numbers, and release filenames are managed from a single source.
Added an in-app update checker and a `Check for Updates...` option in the Help menu.
Replaced the old bundled PDF help files with markdown-based Help, License, and Version History documents shown inside the application.
Added a modern cross-platform build pipeline with generated build scripts, staged release folders, release-note generation, and version-manifest generation.
Added Flatpak packaging as the Linux release format.

Improved processing stability by adding more robust error handling for file loading and worker-thread failures.
Improved file and resource path handling so writable files such as cache and logger outputs are created in appropriate writable locations.
Improved startup and window metadata setup so release information is taken from shared application metadata instead of scattered hard-coded values.
Cleaned up syntax and compatibility issues reported during Ruff-based code checks across core processing and UI helper modules.