Add initial project structure and documentation

- Created architecture documentation outlining high-level design, module organization, data flow, security model, performance considerations, testing strategy, and deployment architecture.
- Added pyproject.toml for project metadata and dependencies management.
- Introduced requirements files for development and production dependencies.
- Set up testing configuration with pytest and tox.
- Established basic directory structure for source code and tests, including __init__.py files.
- Implemented a sample web application (index.html) for drag-and-drop functionality.
- Configured VS Code workspace settings for Python development.

requirements.txt

@@ -0,0 +1,3 @@
+PySide6>=6.6.0
+PyYAML>=6.0
+python-dotenv>=1.0.0